Sad to hear this situation - but I'm also in the similar one. I have a contracted speed of 32mbs, which has suddenly dropeed to ~22mbs.. and the new contracted speed (Im due for renewal in January) is now 21mbs.
BT... what's going on?
I moved your post as other thread was marked solved and this way you will get replies to your specific problem
can you post router stats. If hh6 then advanced settings then technical log information. If hh5 then troubleshooting then helpdesk
can you enter your phone number and post results remember delete number
Try quiet line test dial 17070 option 2 should be silent and best with corded phone
are you using test socket with a filter to see if that helps
It is possible that since you were originally connected the take up has increased resulting in crosstalk. We don't have any idea until you post the reults requested by @imjolly