Incorrect billing & bad customer service

In December 2017 I installed a fibre line through telkom, a 4mbps line at 599pm a promotion at the time. This amount was confirmed to me telephonically, whilst finalizing the contract of a 24month period,as I understand all calls are recorded. I have been experiencing an issue whereby telkom keeps on adding a call catcher amount of +-R160 which is a service I did not request and was not charged at first. However, after a few months it was added to my account and I had to pay more then R599pm.I lodged a dispute and was told it had been rectified and I will be billed correctly going forward, alas after 2 months it began again and I'm now being billed R750 plus pm,despite phoning the call centre and going into the store. I had been to the store today and was told someone would call me, which they did but then I was told no one could assist me as the system was offline, shortly after I receive an invoice with the R750 amount reflecting for September. I refuse to pay for an addition I never requested nor have the use off and I cannot understand why this cannot be rectified. I need help with trying to get this resolved for once and for all or to cancel this contract. It really is not difficult to charge a consumer the correct amount.