Billed for a cancelled contract

I got a call from Telkom Mobile Talk call centre (telesales) regarding a special promotional deal on their 7 inch Hauwei tablet in October 2015. It sounded great and I ordered one and gave them all my banking details for the monthly debit order. I was promised that the device would be delivered within 7 working days. One month later I was still waiting and eventually made enquiries. Again I was promised delivery within 7 working days. When the device arrived however they had sent me a Sony Xperia E1 cell phone. I then returned the phone the next day and cancelled the contract. They then kept on deducting money from my account for courier costs incurred when I returned the incorrect device as well as for a device that I did not have. I had to reverse the charges at my bank account. I kept calling them to tell them that I needed to reverse the charges and that they should stop deducting money from my account. Eventually they acknowledged telephonically that my contract was cancelled. This all happened in October/November 2015 and now on 15 March 2016 they are still deducting money from my account for a contract that was ended and for something I do not have.