It seems that NTL policy has changed recently. If you move to a non-cabled area then you are likely to be held to your 12 month contract.
I think that this has changed recently because you used to be able to cancel immeadiately/or within 30 days.
If you manage to speak to NTL and get your account cancelled before the 12 months is up, make sure you keep an eye out for letters to your old address. I moved to a non-cabled area and I was billed at my old address for 6 months after telling NTL I had moved and agreeing to terminate the account with them. Make sure that your account is actually closed! I wouldn;t want you to end up with a debt collection notice like I did.
(I should say that I eventually sorted this out with NTL thanks to cableforum, but it took about 6 weeks)
J