contract cancellation

Mtn has been billing me for a contract I have cancelled last year already, I have called twice last year cancelling it, numerous times this year and could not get through as I had to hold for more 20 minutes at times<br> I finally got through and this lady says to me that there is no note that shows I have ever called to cancel my contract and she advised I need to pay up before she can cancel my account, I then asked why have I being billed if I did finish paying up my account and her response was that they have been loading data and minutes in my phone of which I never also received, all I want is my contract cancelled why would only my account go into arrears after it was due for cancellation, why was it always up to date? I would kindly like them to cancel my contract.