Overcharged me by R 2 646

I took out a 2 year 8ta contract at 8ta Cavendish Mall in March 1013. It was for 15 GIG at R 249 per month. This was a discounted rate. The full price rate was R 882 per month. I cancelled the contract when it ended in March 2015. Telkom then continued to charge me the full rate of R 882 for a further 3 Months. That is R 2646. The contract had expired and Telkom continued to charge me. I have approached them numerous times to clear up the matter. 4 Months later and nothing has happened. I did not use 1 meg of this bundle, as I had taken out a different deal with Telkom. Nobody has been able to help me, and Nabeelah at Telkom Cavendish has been particularly unhelpful, telling me there was nothing she could do. My guess is that somebody from Telkom \forgot"to cancel the contract. This is a lot of money for me"