Trying to CANCEL contract!

I have been trying to cancel my phone contract since June, when the contract ended, but I don't want the money being debited from my mother's account. I have phoned Vodacom's cancellation line numerous times, and had the account holder email them 5 times to cancel, as well as had someone at a vodacom shop email a cancel query too, and nothing has happened. I need to cancel this contract!