MTN extremly poor service is costing me R1597 a month because Im struggling to cancel my contract

Im trying to cancel my MTN data plan after my 24month contract ended, but is not successful. I went to MTN they told me the system is offline, I have tried to phone them but call centre is useless, I went back to MTN store and they gave me a reference number and told me that MTN will give me a call within 3 working days but im still waiting for them to call me after weeks. After my contract expiered 2 debit orders of R1597 went of. So they are *****ing money on a very clever way. From day one I had billing issues and after alot of hours on the phone and in store they manage to sort it out. Think twice before getting a MTN contract and then think 100 times again. I WILL HAVE ISSUES.