My credit balance remains unpaid

I have a credit balance of about R1600 reflecting on my account. I have been waiting since July for MTN to pay these funds back to me and still have not received my money. When I queried this matter with them, I was told that the delay was due to the fact that they had not deducted the cancellation fee, this was then calculated and deducted from the credit balance but now I am still waiting for the remaining abovementioned balance to be paid back to me. I believe MTN just does not want to pay me back.