Not sure if they are in breach but had same problem like you agreed to continue service and upgrade to 8mb having been told by there
customer service guy I had 10 days to cancell if not happy. My account should hae gone live on the 8th sept 2006 it finally went live on the 10th running at 4mb then on the 12th was upped to the 8mb but still running slower than a dialup!!
I decided at that point i was not staying with them, I sent an email to there cancellation dept requesting urgent contact. I had no call back so the next day I then followed up with second email and finally still no reply by 3rd day i sent email and letter. wek later and no joy plus two attempts to contact by phone and had that put down!!
finally got through by the second week!! and was told by there customer sevrvice they had only recieved one email then dienied all knolledge and told eme I had to prove it!!

what can i say i cancelled my direct debt and waited for them to scream!!