try to avoid BT's offshore call centres
During years of unsatisfactory dealings with BT I realised that I could not rely on the Indian call centre to actually do anything. They were helpful and polite but when I received my next bill, the promised corrections were not there. Instead I emailed the Customer Services boss of BT and was, in turn, contacted by a woman with an Ulster accent who actually fixed things.
Alternatively, use Twitter and when (inevitably) the BT's Twitter Jockeys can't fix issues they may hand you on to online interactive text chat. You then have a written record of your dealings, unlike on the phone.
In the end, increasing fees meant I dumped BT 18 months ago -- so things may have improved/got worse since.