Contract cancellation

I phoned MTN on the 11th to cancel my contract and was told it takes 24-48 hours and they said I must pay the due amount for R413.44 which I paid the 15/12/2015 but still the contract was never cancelled, I then telephoned them again and was told they will send another email to Retentions and cc'd me in it but MTN never cancelled the contract. I called again them again last week the 21 and was told that my account shows a zero balance and they will send another request to their retentions. I called again on the 24 because I didn't get any response and they again told me the same story that they will log a query with their Retentions and I must call Monday. Today is Tuesday and my contract has not been cancelled and a cherry on top MTN debited my account. So what needs to happen to cancel a contract with MTN