Cell c is Taking customers money!

I have wifi contract with cell c, the agreed deduction amount was R289.01 , the past 2 months they have been deducting R306 and when I tried to call the customer service contract number 084 135 no one has ever answered the call. I have contacted this number numerous times. When I took up the contract I didn't choose the option to top up wifi If the one I have finishes so I'm not sure on what reasons my premium has increased and I wasn't even advised about it. I would like to log a reversal of the difference charged for both months and make sure that next month you charge the correct premium R289.01. STOP TAKING PEOPLES MONEY THINKING THEY WILL NOT NOTICE.