Overcharging on statement

In October 2015 Vodacom charged me R20 000 in data cost and when i brought to their attention that i have not been using my simcard they refused to provide me with a report that indicated the usage of that data. Then they came back to me that they will pay me back part of the bill as good gesture and i told them that i was not satisfied with their explanation and that i want all my money to be refunded because i did not use the phone. Well they paid back part of the bill but i am still not happy with that. You will that they will stop from bullying me, yesterday they dedusted again +_ R1000 from account for a sim card that is not in use. I am sick and tired of their incompetence and the arrogance in their members who fail in their duty to proof what they are billing for. This in my view call for a cancellation of contract witout cost because they are unable to keep up their side of their contract. When i request the contact of head of complaints because i am not getting any joy from the people that i am talking they tell me that tjhose contact are confidential. They are a public listed company for crying out loud, they take customers for granted and they are disrespectful.