Change supplier and let BT come after you, see them in court it is the only way to show up their incompetence.
Had problems with our business broadband for 3 weeks, spoke to many people, calls lasting up to an hour, same result, BT test the line and say wait 72 hours. Still intermittent broadband. Finally had enough so arranged for an engineer to call 26th morning, did not turn up of course despite me organising my day around it. Appointment rearranged for 27th called BT twice to confirm engineer was coming, both time confirmed, last call at 5pm unbelievably arrogant basically told me i was being impatient as there was 1 hour to go in the BT working day. Obvious happened, no engineer turned up. Called 6.20 and BT control centre all gone home. Completely useless, I do not believe a word anyone from BT says they are all a bunch or arrogant self centred monopolistic liars. I suppose they will have some sort of standard reply to this post quoting terms and conditions. I pray for the end of our contract so we can get rid of all the BT lines and service including our home lines.
BT, You should be ashamed.