MTN South Africa Billing me extra R3171,6 and refusing to credit it back.

I have a contract with MTN since 2013 and they have been over charging me an extra R16,52 for all the years on three contracts. I picked this up and they are refusing to credit my account, specifically KARABO TLADI, (Specialist- Complaints Management) he tells me I must escalate with ombudsmen not helpful at all. Their services are bad they **** clients extra money for their benefit. And then refuse to refund the funds. It has been a nightmare dealing with them. With no assistance what so ever.