Plusnet fault - no apparent way to report it.... Frustrated!!!

[#1]

I do have internet connectivity - none of the "obvious" faults such as failure to connect - etc.  I have access to the majority of the internet... all the sites I use - except one - from today :  www,ebay.co.uk is unreachable from my router connected to Plusnet - unless I tunnel through a private proxy I have in France.  When I use my proxy, I can establish that www.ebay.co.uk id fully operational - the only problem is that I can't communicate with this site directly.
I've been tearing my hair out with the damned stupid "Jess" who epitomises the artificial about AI - and am frustrated not to find any contact details.
When I follow the tedious troubleshooter - it backs me into a dead end where none of the multiple choice answers is even vaguely relevant.
How do I report the fault with Plusnet connectivity to the internet at large?

Tracepath from plusnet says:
1:  kenneth.local                                        0.108ms pmtu 1500
1:  192.168.1.1                                          0.592ms
1:  192.168.1.1                                          0.328ms
2:  192.168.0.1                                          3.295ms
3:  192.168.0.1                                          3.980ms pmtu 1458
3:  lo0-central10.pcl-ag01.plus.net                      45.023ms asymm  4
4:  link-a-central10.pcl-gw01.plus.net                  46.682ms asymm  7
5:  192.core.access.plus.net                            45.564ms
6:  xe-11-1-0.edge3.London2.Level3.net                  45.563ms
7:  ae-0-11.edge4.London2.Level3.net                    45.472ms
8:  ae-3-3.ebr1.London1.Level3.net                      44.874ms asymm 10
9:  ae-59-114.csw1.London1.Level3.net                    53.472ms asymm 10
10:  ae-11-51.car1.London1.Level3.net                    45.618ms asymm  8
11:  213.206.131.21                                      45.377ms asymm  9
12:  sl-bb21-tuk-10-0-0.sprintlink.net                  115.935ms asymm 16
13:  sl-crs2-pen-0-8-2-0.sprintlink.net                  118.680ms asymm 16
14:  sl-crs2-pen-0-0-2-0.sprintlink.net                  123.864ms asymm 18
15:  sl-crs2-dc-0-4-0-2.sprintlink.net                  121.673ms asymm 17
16:  144.232.10.47                                      132.420ms asymm 18
17:  144.232.5.210                                      152.287ms asymm 20
18:  144.232.11.227                                      150.908ms
19:  144.232.11.178                                      151.342ms asymm 16
20:  no reply
....
This was a problem at 7am this morning and it is still a problem at 7pm.

[#2]

It looks like your router has the mtu set to an old netgear default of 1458. This shouldn't really matter, but you might as well try setting it to 1500.

[#3]

This is what I get and I can connect without problems
C:\Users\Jim>tracert www.ebay.co.uk
Tracing route to www-intl.g.ebay.com [66.211.181.182] over a maximum of 30 hops:
 1    15 ms    84 ms    99 ms  192.168.1.254
 2    33 ms    33 ms    32 ms  lo0-central10.ptw-ag01.plus.net [195.166.128.195]
 3    32 ms    32 ms    31 ms  link-b-central10.ptw-gw02.plus.net [212.159.2.146]
 4    32 ms    32 ms    31 ms  242.core.access.plus.net [212.159.0.242]
 5    32 ms    33 ms    32 ms  ae1.pcl-cr02.plus.net [195.166.129.3]
 6    50 ms    32 ms    32 ms  ae2.pcl-cr01.plus.net [195.166.129.6]
 7    75 ms    32 ms    32 ms  xe-11-1-0.edge3.London2.Level3.net [212.187.201.209]
 8     *       32 ms     *     ae-0-11.edge4.London2.Level3.net [4.69.200.126]
 9    33 ms    33 ms    33 ms  ae-3-3.ebr1.London1.Level3.net [4.69.141.189]
10    32 ms    37 ms    32 ms  ae-59-114.csw1.London1.Level3.net [4.69.153.126]
11    65 ms    73 ms   102 ms  ae-11-51.car1.London1.Level3.net [4.69.139.66]
12    33 ms    33 ms    32 ms  sl-crs1-lon-.sprintlink.net [213.206.131.21]
13   103 ms   103 ms   104 ms  sl-bb21-tuk-10-0-0.sprintlink.net [144.232.24.14]
14   106 ms   106 ms   106 ms  sl-crs2-pen-0-8-2-0.sprintlink.net [144.232.20.138]
15   109 ms   123 ms   109 ms  sl-crs2-pen-0-0-2-0.sprintlink.net [144.232.18.187]
16   109 ms   109 ms   108 ms  sl-crs2-dc-0-4-0-2.sprintlink.net [144.232.8.164]
17   119 ms   119 ms   119 ms  144.232.10.47
18   139 ms   156 ms   138 ms  144.232.5.210
19   141 ms   140 ms   140 ms  144.232.11.227
20   140 ms   141 ms   141 ms  144.232.11.178
21     *        *        *     Request timed out.
22     *        *        *     Request timed out.
23     *        *        *     Request timed out.
24     *        *        *     Request timed out.
25     *        *        *     Request timed out.
26

[#4]

Quote from: ejs

It looks like your router has the mtu set to an old netgear default of 1458. This shouldn't really matter, but you might as well try setting it to 1500.

Genius!
The reason it was set to 1458 is that it is an old netgear router.  I'd never changed the default - as it has always worked until today.
Set to 1458, I get no connectivity to www.ebay.co.uk - and with it set to 1500, everything works flawlessly.
I half-suspect that there's some deeper issue - but, at least, now, I can pretend it is fixed.
Many thanks.

[#5]

That is strange, I am currently using MTU=1458 on my Netgear DG834GT as that gives me the best performance AND the least problems accessing the eBay login page, and I use eBay for hours every day and am currently logged in using another browser tab.
My trace to eBay is -

$ mtr ebay.co.uk
                                  Loss%   Snt   Last   Avg  Best  Wrst StDev
  1. my-gateway                    0.0%    10    3.0   1.4   0.9   3.0   0.8
  2. lo0-central10.ptn-ag03.plus.  0.0%    10   19.0  19.3  15.4  28.5   4.7
  3. link-a-central10.ptn-gw01.pl  0.0%    10   15.8  15.9  15.1  17.6   0.7
  4. xe-8-2-0.ptw-cr01.plus.net    0.0%    10   15.3  16.9  15.2  26.9   3.6
  5. te-4-2.car5.London1.Level3.n  0.0%    10   20.2  70.4  20.2 210.5  62.9
  6. ae-11-51.car1.London1.Level3  0.0%    10   22.9  98.1  19.8 223.2  84.1
  7. 213.206.131.21                0.0%    10   16.5  17.9  15.3  34.7   5.9
  8. sl-bb21-tuk-10-0-0.sprintlin  0.0%    10   87.1  92.9  86.4 109.5   9.1
  9. sl-crs2-pen-0-8-2-0.sprintli  0.0%    10   88.6  91.7  88.6 104.6   4.6
 10. sl-crs2-pen-0-0-2-0.sprintli  0.0%    10   92.8  92.4  91.9  92.8   0.3
 11. sl-crs2-dc-0-4-0-2.sprintlin  0.0%    10   92.6  92.7  91.8  93.5   0.5
 12. 144.232.10.47                 0.0%    10  102.7 103.4 102.4 105.3   0.9
 13. 144.232.5.210                 0.0%    10  122.7 128.6 121.7 186.3  20.3
 14. 144.232.11.227                0.0%    10  122.2 131.1 122.2 169.3  17.6
 15. 144.232.11.178                0.0%    10  122.5 124.1 122.1 135.4   4.0
 16. ???                          100.0    10    0.0   0.0   0.0   0.0   0.0

[#6]

Your computer may detect the lower mtu of the router, and the router can adjust a value (MSS) in a certain type of outgoing packet (TCP SYN) if it was originally too big. I found any performance difference due to mtu size was non-existant / too small to measure.

[#7]

I tuned my modem/router using http://www.dslreports.com/tweaks
to ensure a "transfer efficiency" of 100% and achieve the highest "transfer rate" by trying lots of MTU values.
The MTU values that give my current setup the best throughput are 1458 or 1430.
1500 on PPPOA gives less than optimal results due to 'packing' bits used to fill the packet frame,
and IIRC an MTU of 1478 is the theoretical optimum on UK ADSL PPPoA connections.

[#8]

I hadn't retested fiddling with mtu settings for a while, and my broadband is currently working at an all time high speed. I was aware of the horribly complicated atm cell packing calculation. An mtu of 1478 might give an extra 5KB/s over 1500, but 1458 and 1430 were not much different to 1500. I could get another extra 5KB/s by turning off tcp timestamps to save 12 bytes per tcp packet.

[#9]

My various versions of Linksys WAG54G all worked well at 1500,  my current Netgear DG834GT doesn't entirely work well above about 1470, and the maximum my Draytek 2710 can be set to on PPPoA is 1492 !, but all needed tweaking to get the optimum results.
Which reminds me I have a Billion 7800 arrived from eBay that I need to connect up and MTU tweak !

[#10]

I just changed the mtu on my computer, sjh641 could also have tried changing their computer's mtu to match that of the router.