Unfair treatment by Cell C

Good day, I hope you can help. Cell C has done multiple debit orders on dates that I never agreed to in accordance with my contract causing me to incur extra costs with my bank. I have called a multiple times only to receive empty promises as to fixing the problem. They have also debited twice on the same day on multiple occasions when my account was in no arrears and promised that they would never do a debit order for the following month because they acknowledged they took double the amount on a single month stating they are not sure as to what could have resulted in that only to find out that they did take the money. It's been more than 6 months calling trying to fix my problems and all I get is empty promises over the phone really. I had to find out that they have changed some terms of my contract without even noticing me prior to doing it. I need help. All I want to do right now is terminate my contract because I believe they have done a gross breach of the terms. I also want my money back as they debited double on multiple occasions. I have 7 months left with them and I am afraid they will keep doing this until the end of the contract, which I cannot afford. Nobody has helped me when I called, instead my problems keep persisting. I would really appreciate your assistance. Thank you, and I look forward to hearing from you.