Fibre speed drop

[#1]

Can some one pick up Question #118741537 please?

My fibre speed is much lower than when it was installed  - now  3.42 Mb/s according to BTW best effort
Plus Net Stable rate page reports:
Telephone number:
    01535
Phone exchange:
    CROSS HILLS
Estimated line speed:
    10Mb (This may vary between 5.1Mb and 10Mb) - Checked on 2016-01-03 13:20:02
Current line speed:
    3.6 Mb .
Not been any changes here at home and the line sounds clean enough. I  have the BT Openreach Huawei HG612 3B VDSL/FTTC Fibre Modem and a Thomson Technicolor TG582n FTTC  which I flash upgraded myself as the supplied router was awful .
I am approx 1.1 miles from the green cab.
Home wiring is in good order ( there isn't any!) and all arrnagements have been the same since installation when initially I was getting 11.mb/s . After a while usable speed settled to between 9.5 and 8.5 Mb/s. Now it has fallen to 3.5 
Over the few months it has been working there has been the odd power cut and on reconnect has always synced at between 8.5 and 9.5 Mb/s
Thanks
G

[#2]

Pending a response from Plusnet, could I ask, how long ago was your fibre installed?
Also,

Quote from: gpsmout

Over the few months it has been working there has been the odd power cut and on reconnect has always synced at between 8.5 and 9.5 Mb/s

How long since the speed dropped from 8.5/9.5 to the current 3.4 level?

[#3]

Fibre has been active since mid July , so 6 months.
Its been slow about a week.

[#4]

Ineresting that repsonse times to faults  when phoning tech support are given as 72 hours minimum  but when you report a fault on line , the first response time quoted is 24 hours. Could this be clarified please?
Anyway thanks to the agent who agreed to look into my fault before the 72 hour wait is up.

[#5]

Problem solved after very quick repsonse from Tech support who clearly understood the problem and was able to reset line profile to maximum available within a very short time. Excellent result .