My bill was double the amount

The worse kind of customer service, it's been 3 weeks taking me for a ride. They've over charged my account and each time I call they confirm the error and say they will call me but I end up calling them because they never call and haven't fixed my issue. They've charged me double and to date since July haven't sorted the issue and don't bother to call me but I must always call. All team leaders and consultants don't have answers.