Vodacom Overcharged me for their Mistake !

I called vodacom retentions at the beginning of November to upgrade my contract to a sim only deal. I was told that it has been done successfully and i was even a monthly amount . I kept getting calls after that still from Vodacom saying that i must upgrade my contract and that it is not upgraded. So I've called again on 26 Nov and spoke for over 1 hour to do the same thing again, the vodacom consultant told me that the previous consultant didn't upgrade the contract, she just added some bundles. So after an hour on the phone with the vodacom consultant, i was told that now the upgrade is done. Now month end, i get a ridiculous bill of R2000 more than what I'm supposed to pay for because the first consultant has made a mistake with the upgrade. I callled today again, after holding for almost 30 min, the call just gets cut, i need assistance asap and i need a credit for vodacoms error. I can't pay for the unprofessional staff mistakes!