Overcharge for mobile data

I received an unusually high mobile data account which I queried with CellC. I have had my contract with them for 14 years. Whenever I needed extra data I bought the bundles. Since last week I have been going back and forth trying to explain this to the agents who kept giving me the run around. Whenever I got to the cancellation department I was begged to retain my account and was told that the problem would be sorted out. I buried my mother on the 1st December yet I have data usage for most of that day! Yesterday an agent eventually understood my gripe and was going to reverse the mobile data charge, but when it went to the back office they refused. I was on the phone with them for probably an hour or so and I even spoke to a manager but to no avail. In the past when I bought data bundles, I lost a lot of data because I couldn't connect to the mobile data which I queried with CellC as well, but yet again, no assistance! I have now cancelled my contract with CellC as customer satisfaction is truly not part of their repertoire! I am extremely disappointed in their service levels and their lack of comprehension!