Failure to issue paid up letter and refund customer for over paying

Cell C has the worst customer service experience ever. I called in to cancel my contract and get a paid up letter issued, I was then quoted R9789.67 which I was told the payment takes about 2 working days to clear and I will receive my letter then. I followed up and was told that this has been done however I overpaid by R7000 and the team is working on my refund. To-date I keep being transferred from one department to the next even after quoting reference numbers which I would think make the job of the agent easier but not in this case. All I want from Cell C is my paid up letter, proof of contract cancelation and my refund. I don't know how many customer acts have been broken by the service provider just on this one case alone. If anyone knows where I can take this higher please let me know.