contract ended but I am still being billed

My name is Dionne, I have a contract with telkom/8ta, I requested for my contract to be cancelled and closed but they have not closed it. My contract passed the expiry date and I am still being billed! I have sent out cancellation form in October 2015, it is January 2016 and my money is still being deducted, I have contacted them several times about this after they told me that it shall take up to 21 days to be cancelled and closed! They are still requesting a bill of R900 and something rand and I fail to understand why they don't want to cancel my contract. The two year contract has expired last year already but I am still fighting to cancel my contract! I have never missed payments and I am a loyal customer of the! Now they are playing with my money now. I'm so upset!