Takes money monthly but I am not a customer!!!

Two months ago, I paid R18 000 for an early termination of two contracts with MTN due to incorrect billing which was never resolved. The contracts were terminated and the numbers ported to Vodacom. However, MTN continued to debit my account. They now owe me R1 709. It reflects as a credit. I have asked for this money to be paid back to me for a month and they have not resolved this. I have six reference numbers which have been escalated. I phone every few days only to be told a decision has not been made. The money is owed to me. It was *******ly taken out my account after I terminated the contracts and paid the early termination fees. The call centre agents cannot help as they can see the credit but state that because I am not a contract customer and because I am also not pre-paid, they don't know which department this belongs to and cannot do much more than escalate it and issue me with a new code. What can I do? MTN please call!!!! Please Resolve this. My number is ********** 556. I cannot even give you the contract numbers as they belong to my children and they do not reflect on your system anymore.