Cancelling a contract

payless

I am in dispute with a mobile phone provider , over services supplied on a particular contract... believe I am entitled to cancel contract due to their continuing errors / mistakes and keep the phone ( which was expensive even with a contract) well I have actually sold the phone... but wanted to use the sim for something esle , but even though the contract/ website says these services are available on that tariff they still say its not

Can't understand why mobile firms are allowed to provide info on credit files, as they have me over a barrel ... if I cancel DD (, because I feel I'm in the right , I'm happy to let the courts decide , if they take it that far ) they can register a missed payment , which for me is a no- no, so guess I'll have to take them to court instead!