The appalling service received

I am using this platform as a last resort. I have in my possession documents proving that I have been billed incorrectly for the 2nd contract I took out with MTN in May 2015. I had hoped that by going to my local MTN store(Liberty Midlands Mall) I would be able to get this resolved. As I do understand mistakes happen and I just wanted my money refunded. I started the complaint process with them on 10 October 2015. I have been into the store and made numerous calls to them to follow up and to date I have had no joy. I have sent emails to the service email address they have and have not received acknowledgement of my emails let alone a response. When I sent my daughter on my behalf to the store on 7 November 2015 they advised the matter was escalated to the highest point and I would receive a call within 7 days to resolve this matter, I still await that call. I do not understand how a simple request from a loyal customer of 12 years could be treated in this manner. Had it been me owing them, they would have demanded that I rectify the matter and I am now asking for the same courtesy.