you should call them up and tell them they are breeching their service contract and threaten to call a lawyer and whatever your equivlent to atorney general is....that will get'em moving. That or dump them for the competitor.
I can't, it's a problem with the dsl component of the telephone line at the telephone exchange. The ISP doesn't own the line or the exchange, British Telecom does. So even if I changed ISPs, BT would still need to fix it and any new ISP that I had a contract with still would need BT to fix that for them. I cannot go straight to BT as their contract is with my supplier, i.e. my ISP.