UNPROFESSIONAL CUSTOMER SERVICES

I received a call from cell c consulted n offer me a sim card data and we agree on the bill she was talking about so my problem now I received a bill statement and the amount is threeple of the amount that we were agreed. I try to call cell c the thing that the are explaining to me it looks like they want to rob me day light because in a month end half they bill me R790.00 and on a agreement it sad I should pay R149.00 per month.