Vodacom's Service is Truly Lacklustre

Last month (End of May), i was incorrectly billed by Vodacom. Upon making a follow up with them, i was told that somebody walked into the Vodacom Shop and upgraded my data contract. I told them it wasn't me and I even faxed the affidavit and ID documents as per their request. It's been 3 weeks now and Vodacom hasn't refunded me my money and they also haven't reversed the upgrade. I'm really at my wits end as what to do now. Can somebody from Vodacom help. Now June is coming to an end and they will bill me again if this doesn't get corrected.