Ntl saying they have lost the number may relate to some weird computer fault, in that if somehow a database dropped it, as it came from a BT range, it gets resent back to them for reallocation if it becomes inactive
Anyway, it's clear nobody at ntl has grasped your problems. That's not good enough. Cable Forum has high level contacts within ntl that have been good at troubleshooting these sorts of issues. If you want us to get them involved, please PM me some details (your account name, account number, property address, the phone number that got disconnected, a daytime contact phone number - mobile?, email address, and any other information that can help our contact sort you out).