Cell phone contract over billed

I took out a cell phone contract about 3 months ago at telkom killarney, the initial contract was R369pm and I made it clear that I want it on top up, as im buying the phone for my daughter. First month I was charged about R580, It didn't really bother me cos I know they might've charged me a pro rata. Seocnd month I was debited R1870, I went to telkom and enquire, I was told it was a mistake and they have rectified the mistake. It is now the third month and I was debited R1899. I went back to telkom store the consultant could not explain why I'm being charged this ridiculous amount, I ask to speak to the manager as angry as I was, he refused to speak to me. Our agreement was, I pay R369pm not more than that. I was assured when I sign up for that contract that my bill wont be exceeded. Is this the service telkom is giving their customers? I have no intrest in continuing with this contract as they have *****ed me. For all I care, telkom can take their phone back and cancel the damn contract.