im lost my internet is capped at 2megs?

[#1]

Im at a complete loss

if anyone can help it would be really appreciated

firstly let me explain my situation

3 standard pcs and one laptop+xbox and wii
one pc is up stairs in the  bedroom on wireless
two are in my living room on cable  and the laptop  is not  being used atm but when it is,  its on wireless
xbox and wii are both in living room on wireless
normaly only two of any of the above are used at any one time and  while I think about it I cant acctualy think of a single occasion of more than two being used  but it might of happed
I recently was upgraded to 17 megs and before it was upgraded  it felt like my internet was slow then speed  up like a car accelerating it has always felt like this  even when I was on a 8 meg connection it would also be so slow that I could lag for 10 secs  then suddenly it would all work then  lag again almost like it was changing gears and after maybe 30 secs it would be ok
before my internet was upgraded  I decided to  try to fix my speeding up internet
after talking to  customer support  and I explained that my router was on a 15meter cable they said  this problem might be fixed by  moving the router to where the  phone line came into my house
so I spent £80  for two wireless routers  and moved the  router right next to where the phone line came into my house
but  this did not to fix anything in fact two pcs could'nt even pick up a signel  so I was acctualy a bit miffed that id spent so much for nothing(i also had a spare newer router but this was even worse  as I could only get a signel on one pc)
and with it not making this situation better I just put everything back the way it was and was going to live with this problem
but now im finding my internet is capped at 2megs after speaking to customer support and checking online  everything appears correct and im reciving 17 megs to my house  even from testing sites it all says im getting 17 megs
but somewhere along the  way  im only getting 2megs to my pcs
and if I am watching youtube on one pc the other pc  suffers from slow net
at first I was thinking it was just a slow site  but ive notice for a month ive not downloaded anything faster than 2 megs
from steam to guildwars2 to bbciplayer every thing I download is only at 2 megs 
but it is always 2 megs so I can stream constantly which is different to before  where it would speed up now it  is always  2megs

I have kaspersky pure on my  pc  but ive not changed anything on it for years  only updated profiles
other than  that it is  a  bog standard pc full of games
my pc specs are

intel q6600  2.4megs
4megs ram
1 tera byte hdd with roughly 300 megs left
x-fi-sound card
5850 graphics card
yeh its a old pc but still plays everything good enough for me
my other two pcs are very similar specs  but I think they both have 200-300  gig hdd
but both have  better g/card
all 3 pcs feel like we have a signel 2 meg connection  if I watch  youtube on mine then the other two will have streaming  stutter on theres
all three have kasperskys  and all three are windows 7

so to recap
1/ my internet has changed from a speeding up internet to a solid capped at 2 megs internet  even though ive not changed a single thing in my house
2/my internet still is on a 15 meter cable
3/and the change from the speeding up to solid capped internet happed about a month after my internet changed from 8 meg to 20 meg
4/my internet is ment to be unlimited
any ideas what could be causing this problem like the man from plusnet said it appears to be a problem on my side so im wondering if I have in someway changed a setting or something to cap my own internet to 2 megs and what it could be

[#2]

Hi zimboy69,
I've just ran a few checks and the BT profile and our profile are both showing as 16800Kbps.
When you say you can't get more than 2 meg, do you mean 2MBps or 2Mbps as the B is Bytes and the b is bits. Your speed should be somewhere near 16Megabits per second. If it is only 2Megabits then I'd suggest raising a fault here. If it is 2Megabytes then that's about right.
You are on unlimited by the way.
Jojo

[#3]

To add to what JoJo's said: when downloading files most software (e.g. browsers, P2P/torrent software) displays the speed in Bytes per second.