Vodacom can't stick to agreements

Few months I agreed to an upgrade after vodacom was willing to cancel the rest of the old contracts amounts after a previous mistake by them regarding whether a phone was dual Sim or not. A lady by the name of Amanda helped me upgrade, and for 3 months they breaking this agreement, by charging me for the previous contracts! I have sent Amanda an email to which 2 months later I'm still not getting a response