Overbililng - no results on queries

I have now tried 6 times to get a response from MTN I need. I have a separate 5G data contract (apart from my phone contract) and for 6 months I have never been able to use all 5Gs and all of a sudden I receive a bill for almost R2000 for extra data used. After several queries via e-mail and their call center, they have not sent me a detailed list of data used. I need to know how this happened and yet they can't tell me. I subsequently stopped the debit order at the bank as I know MTN will just take the money without thinking twice. I then paid my phone account, in full, via the internet. MTN has now proceeded to suspend my phone service as well as my data service for the outstanding R2000. I don't mind them suspending my data contract but now they have suspended my phone service to such an extent that I cant' even receive calls or SMS's. I keep on telling them that my phone contract is paid and they have no right to suspend my phone service and they maintain it's on the same account number and holder and therefore THE SYSTEM will suspend the service automatically. I have no idea what to do anymore. Unfortunately my contract is valid for another year. What can I do?