Over charges

Good day<br> <br> Kindly assist me please. I have a contract with Cell C.<br> They are over billing me for no reason.<br> I have 2 contracts with them and the one contract did not receive the R100 it's suppose to receive every month.<br> I have put a limit on the second contract and even with that they are still over billing me.<br> <br> Please advise me of ways I can get out of the contract. And also be able to get the over charges back.<br> <br> I have sent over 8 complaints to them and no one seems to be able to assist.<br> <br> Thank you