Failure to Cancel Contract - Still Being Billed

In December I called Telkom and they confirmed I could cancel my 10 + 10 gig contract by January. I took the cancellation letter into Greenstone branch and it was processed. I have since received statements and been billed in January and February, and again an invoice today. This is after calling the call centre various times and confirming it's been cancelled. Last I heard, the cancellation note appears on their system but they CANCELLED the cancellation for some unknown reason. No feedback after the call centre confirming this was done. From December I had purchased a bigger contract 50+50 so am being billed unnecessarily. I request that this is urgently sorted out, cancelled, and refunded from January until now. This is now urgent.