Charged for a service that was discontinued

I upgraded my contract after the upgrade date and as my existing contract type was discontinued by Vodacom I was forced to go onto a different plan. Vodacom then charged me R540 for migrating to a different price plan. After being on the line with customer care and then the upgrade department for an hour yesterday I was assured that the accounts department will phone me back at 08:00am yesterday morning - I am still waiting for the phone call. I do not see why I have to pay for something that Vodacom has forced me to do. Not only am I paying for something that was decided by management, but I was not informed that I will be charged for going onto a different contract when I did my upgrade. I want this reversed from my account IMMEDIATELY!!!!