Taking MY money even though I have cancelled

I have been trying to cancel my Vodacom contract for months now. I have signed all the documents sent to me by Vodacom and returned it to the Retentions division. I do not owe any monies on my account either. I have sent the documentation 3 times now and still they continue to take money from my account. The service is disgusting. You cannot tell me that they are not receiving the documentation. They are just not doing their jobs!!!!!!!!!