Upgrade cancelation request

Vodacom disappointed me lately. I've been using their services for more than 10 years. They called me for an upgrade offer a month back. I accepted their R99 offer then after a week I called them and requested that they cancel the upgrade immediately. They agreed but on the debit date they debited a lot of money that I didn't agree upon. They didn't even debit according to the upgrade. I called them again they promised to correct the error but even today nothing happened. They still billed me incorrectly. I called again but the consultant couldn't resolve the issue only promised to call me back. I've been waiting for the call since. I need help really