Cancelling of contract just not happening.

I have been trying to cancel a contract for an unused number for the past 3 years. First telephonically while upgrading a different contract (all under the same statement details) I have been to the MTN branches twice. I have signed the forms. I have emailed and have had responses saying the contract has been cancelled, But I am still being billed and the number is still reflected on my account. THIS is UNACCEPTABLE and extremely poor service. What else can a person do!!!!!!! Never mind even trying to get credited for the amount... A reference number apparently also mean NOTHING.