Overcharge on data contract

I have a data contract for R209.00pm. I have been billed R994 this month apparently because discounts were not app****. I have been trying to get this sorted out for 3 weeks now and cannot get anyone to help me. I have been promised a call back 3 times and I am still waiting. The debit order has now gone off my account for over R1000 which I cannot afford to pay. The service is absolutely disgusting. I want this sorted out urgently