Had enough of VODACOM

Absolutely Pathetic!!! How difficult is it to cancel a contract and the debit order that goes with it? This is the 4th time I am bringing the issue to Vodacom's attention via Helopeter. My mother's cellphone contract was cancelled years ago, but the debit order goes off every month. At the beginning of April, I had to send her bank statements so that Vodacom could see that the debit order is going off. They then allocated the monies paid into a cancelled contract - bit of a cheek and promised that the debit order would be cancelled. Well the money went off again. What must I do?? Vodacom is robbing a 93 year old lady.