Impossible to cancel On Air TV contract

On Air Tv do not even earn one star for me! My mother who is a pensioner took out a two year contract with them for an extra DSTV decoder. She is still paying even though the two years passed already. She contacted them to stop the debit order and even stopped it at her bank. They even now take two payments per month and have the audacity to send her sms's if there is not enough money in her account available! It is impossible to get a statement out of them. I also found out from Standard Bank's help desk that it is impossible to stop the payment going through from their side, because they change the date or change something in the reference. The date part I know is true, because you never know when they take the money and I also determined that they use different account numbers: OA-***. I would like to have a copy of my mother's contract with them as well as statements and a way of cancelling this contract once and for all.