Refund of debit

Had the most terrible experience with mtn, I have taken out a laptop contract with them 2 years ago and it has been settled in July this year, they still debited my account in August with the usual monthly installment and after calling them numerous of times regarding this debit I was told that they will need to look further into it and will get back to me within a day, this was an ongoing issue for more than 3 months and still haven't gotten any feedback from any of their agents. This use to be my favorite network but the lack of communication and help has really made me think otherwise.