Incorrect Billing

I had a contract with CellC from June 2017 for a Router with a monthly instalment of R199 and not as an open contract but fixed contract but for my surprise CellC is charging me more. 1st of July they charged me R296, August R279 and September R279. I did log a complain on their website but unfortunately no one border to come back to me. I am now 3 months in this contract but I do actually regret myself. Cellc service is very poor. I even went to Mall of the North branch to complain about this and they told me that it was because of the other Simcard of which I have never even used once. They said to me it has been cancelled but I am still paying what I’m not using. I am so fed up with this poor service and *********** of CellC. Could you kindly please refund my money back or otherwise I am cancelling this contract because is so useless