Permanent speed drop after one day of use...

[#1]

Hi all,
I have been with Plusnet for 1 month and so far its been a very frustrating experience. I had the standard value service at first which was giving out great speeds for my needs (~2.5Mbps) for a day and then suddenly dropped to 0.1Mbps. I reported the problem and tried the usual master socket tests and was told the line had stablized after giving out some errors but I never saw an increase in speed. After putting up with near unuseable speeds for 3 weeks I decided to upgrade to the fibre option to hopefully sort the problem which was installed on friday. This gave out a speedtest of 36Mbps which I was over the moon with - considering I was estimated to get around 27 on my line. Today I go to use it and it is running at 0.2Mbps again and doesnt change.
I even asked the engineer strip out all the old extensions and only go to a new master socket to rule out the possibly out dodgy wiring inside my home...... surely there is something going wrong with the wire to the exhange or something?
Has anyone else experienced this? I used to have cable internet which just worked and never fluctuated in speed or dropped, I really dont want to have to leave plusnet as they have been great in every other way!
Thanks in advance!

[#2]

What does this https://portal.plus.net/my.html?action=data_transfer_speed say for your Current Line Speed. I believe that for Fibre accounts it should be set to 40Mb. There have been occasions where after initially being set to 40Mb it has changed back to pre-fibre values. If its set to a low value then give CSC a call and ask them to set your PlusNet profile correctly.

[#3]

Yep you're right, a quick call this morning to customer services and the helpful man reset my profile and told me to wait 20 mins.....  back to full speed again! 
He said the profile was actually set to 0.2Mbps!!