Billing complaint

I'm very disappointed with the level of service I have been receiving from Vodacom they keep on deducting incorrect amounts which is not stipulated on my contract and whenever I log queries with the call center they always promise to refer the matter to Billing department and they promise it is resolved but then same error happens again the following month, so I've been sent from pillar to post with no solution to the problem. If I don't receive a positive response within 72 hrs I'm handing this matter over to my lawyers.