MTN SA, NO NO NO

We have used MTN contract phones for 19 years. Last year, my son paid the cancelation fee around September 1st and got off the phone. By chance, I found out that MTN had withdrawn money every month until June of this year, so I requested a refund from MTN through the Brooklyn branch, but they did not resolve the issue even after 3 months. They said that the MTN headquarters agent who first received the application mishandled the matter, and MTN cannot take responsibility. I have serious concerns about MTN's governance. I want MTN to return the unfairly earned profits to me.