Incorrect Billing!!!

Signed a new mobile contract with Telkom on 26 July 2015. The contract price for the Smartplan 50 for the Samsung Galaxy A5 was R269. The first month we were billed in excess of R500 and an amount of R299 every month thereafter. Upon our 1st query regarding the discrepancy in pricing, we were told that the adjustments were made and we will be credited accordingly (this was after some harsh words from my side as the assistant in store refused to assist). A month later and there were no changes with the billing. People at the call centre were not much help either. Nobody can explain the amount of R299. A second visit to the Telkom store and we were advised to speak to a team leader at the call centre and still no joy. We would appreciate if somebody with an idea of how Telkom contracts and billing works look into the matter and solve this issue ASAP.