CANCELLED MY CONTRACT IN NOVEMBER AND STILL BILLED

I cancelled my cellphone contract with Telkom as I cannot afford the bill and Telkom is still debting my account. My cellphone contract came to an end in November 2015 and I went to the Telkom office in October to cancel my mobile contract. I completed a form and the consultant advised that it would be cancelled. I got a call from the Telkommobile office to say that my contract has been cancelled and now Im still being billed. How is this possible??