MOBILE ACCOUNT DISASTER

I've been dealing with a Michelle and Stephanie since the 16.10.2015. I was advised by a sales agent about this awesome deal for R99.00. Last month i received a bill for R900.00 i requested an itemised billing doc which i received, I then asked Michelle and Stephanie if they could please listen to the recording between myself and the consultant as there was no mention that the account would be open and could occur further data usage. They were gong to send me the information, which to date i haven't received. They also changed it on their side so that i would not pay extra data usage, this month i was debited another R280.00. I've left messages for Michelle and Stephanie and sent and e-mail to support. Still nothing... this is a *******, how do i cancel this contract???