Billing and Customer service

I have a major issue with Cell C, they incorrectly debited my account on 1/11/17 after cancelling my contract. I took this issue up with their retentions and customer service department at the beginning of November 2017, one month later and this matter is not resolved. They said that they will process the refund and the consultants say they will get back to you with progress but weeks pass by and no one contacts you.