I have been having trouble. Tiscali later Talk Talk used to provide an advanced voicemail feature (for a cost) which enabled me to collect messages from afar using a dial in and pin number. The service stopped working in March. After several calls (for which of course I had to pay) I established that the service had a technical problem which would cost too much to repair so TT were not offering it any longer. I asked about a refund and to stop paying going forward and was told charges would continue unless I chose to downgrade, which would mean a separate call on a separate number. Instead I wrote to them (I didn't have another hour and a half to spare - writing was quicker) and received an apology together the promise of a refund plus ten pounds. Of course, the next bill came and included neither the refund nor the tenner, but an additional charge for the next month's non-service. I phoned about this and was told that as the person who wrote the letter didn't have the authority to do this the charges would stand.
I have cancelled my account and moved to a different provider (not BT - that was too, too painful) and reported TT to the Ombudsman who has accepted the case. When my final bill arrives, it won';t be paid without several deductions, including for my time. I am a professionally qualified person and charge my clients by the hour for the services I provide, based on my intellectual knowledge and skill. I will charge TT at the same rate and this means they will owe me. I have no qualms about going to the small claims court if they refuse to settle and recomend that approach to anyone.