If you have a fault on the line then switching providers won't fix it, If BT are your provider then contact them and raise a fault, explain it's happened with 2 providers and when you switched the problem continues, so that should rule out equipment as you would have 2 different hubs.
The lines belong to Openreach, It's them who would come out if a fault needs fixed.
Do you have normal broadband or fibre broadband?
Is there any noise on your phone calls? Dial 17070 and select option 2, there should be no noise between the announcements.
Are you using the test socket with a filter to see if that helps your connection - even if you have a filtered faceplate
can you post stats from your router. If hh6 then advanced settings then technical log information