Bt infinity bandwith issues

We live in County Durham and are not very IT savvy.We have had BTInfinity without any issues for 11 months with regular speeds of 35+ Megs. Since the start of December we have not been able to stream ( BBC Iplayer says insufficient bandwith ) or connect to secure web pages and constantly having to refresh pages. To cut an extremely long story short we have had 50 + phone conversations with BT india and 8 seperate open reach engineers who have replaced everything and found NO problem at our end. Speedtest.net cannot complete tests ( the download speed slowly drops to zero ). BT speedchecker shows 36+ megs.
Has anybody encountered this problem and know the solution

One post is enough. No need to spam the forums.

sorry , not my intention to spam just to make sure that in my desperation to find a solution I reach the right audience

What does the speedtester.bt.com say exactly, especially your IP profile?

Sorry took so long to reply but everything takes ages at moment as have to constantly refresh or close down internet explorer
I did a test about 30 mins ago and tried to post results with my original post but had to refresh and lost original post

download
test achieved 30***
IP profile was 36***

upload
test achieved 1400
IP profile 2000

can't remember exact numbers but will redo test when it allows me and post results

Have you tried a different browser, like Firefox or Chrome?

If the issue is congestion, rather than some other technical issue then after about 2am and before 9am one would expect things to improve significantly - do they?

Yes, same happens with all, makes no difference

time of day makes no difference- wife been online at 6am on a sunday morning

Just curious but what is your MTU setting set to on your settings pages?