Account cancellation

Hey please help, in April 2015 I called my service provider MTN to ask for cancellation of my contract with them, which was already expired at the time. And about a week later, I made a follow up on my request for which I was then told there delays on the service because of the strike during that period of time, I was then advised to wait for about two to three weeks for them to process because of the delays. I then there for went to MTN desk to request for the number in question to be suspended because I was not using it at the time, and the number suspended and since then I never heard from MTN for the update. Now my problem is that, I am receiving letters from the attorneys telling me I must pay R 1200 for a contract that was supposed to have been cancelled long time, and if then It was not cancelled why was I not informed and to be told the account was in areas for the account that had been running for six years with no problems and on cancellation to be told it's in areas, I find so strange for them to tell me I'm owing the account they've been doing debits from my bank the whole 6years running with no problems. And now nobody seems to be willing to help me @mtn with this.