Vodacom doesn't want to cancel my due contract.

Hello Peter. Please help me out, I've been trying to cancel my contract because I've reached my 24 months with Vodacom. They keep biling me. My contract should to be cancelled already, I started calling in on August to cancel, and they keep saying it has been canceled but every end of the month they deduct R590.86, I'm dealing with ******, when I call the upgrade/deactivation center they always say my contract has been canceled. Please intervene because the next thing they are gonna rush into blacklisting me, because they have the power to do so. I'm tired of paying this ***** company, this is so unfair and unjust of Vodacom.