Vodacom contract cancellations impossible

I am trying to cancel one of my Vodacom contracts. It is apparently impossible to do. I am still being billed for a phone I cancelled in Augsust, and the line is still active. I can also not get through to their call centres using the numbers 082 135 and 082 137. I'm thinking of cancelling all my contracts with Vodacom and then to return every debit order until they get the message.