I totally endorse your comments about the useless customer service - despite Mr Dunstone's assurances that those problems "are behind us".
My experience has been similar to yours - in my case broadband was pretty awful initially until i got a decent modem/router. Tried several times to get anyone to help via the helpline - but gave up due to the long delays. Sent emails but they even took a week to reply to those - by which time I'd sorted it.
It stayed fairly reliable until they revised me to an unbundled connection. What this means is that, instead of BT terminating my line on their DSLAM and forwarding my traffic to TT via BT's ATM network, TT now rent the line from BT, put their own terminating kit on the end (at the BT exchange) and carry my traffic totally from there on their own network. (Has this happened to you? You can check by calling the operator on 100)
Since that happened, everything's been screwed up. Broadband often won't stay up for more than a few minutes - and even when the modem connects, there is usually horrendous packet loss on the transmission so it's virtually unuseable. Even the voice line is unreliable - with clipping, distortion and silent periods (speech missing). After waiting a week to get a "standard text" reply to an emailed problem report, I finally decided to write direct to Mr Dunstone - setting out in detail my complaints - and my view of the likely cause (basically - not enough equipment to ocope with the traffic !)
Well - that was nearly three weeks ago and - surprise - I haven't heard a thing. I'm about to do the same as you (viz: cancel) - but you must ensure that you have EVIDENCE not just of their poor performance but also of their NEGLIGENCE - otherwise you'll get caught for an early termination penalty. (Read the hugely long terms and conditions). You must also write to them and give an ultimatum that if the problems not sorted in say 14 days, you will terminate and claim the costs you have incurred as a result of their negligent and incompetent advice. You should also write to OFCOM - or copy them in on the correspondence.
I'm going to take some legal advice - and will keep you posted. However, I think you could prejudice you case by cancelling the direct debit - indeed, your bank will probably tell you that you must get the "supplier" to cancel it.
Good luck anyway......
i have been with TT FOR 10 WEEKS? NOW AND HAVE BEEN PREVIOUSLY CONNECTED TO TT using my dsl phone line whcih i uesed with AOL dial up and the ethernet connection supplied. however i powered off all computer and modem 4 weeks ago. tried to connect wont work. apparently he had(talk talk help line) connected me via the internet because the disc wont work. so they had me buy a 15ft ethernet line still no joy cost 15