Incorrect Billing and Poor response

Mtn has incorrectly billed me for promotional Data. In June 2020 I had purchased promotional data on the MTN Cake crush site, I had paid for the 3.5 gigs data with R 99 of my own airtime. Mtn, however, billed the 3.5 gigs to my account which by the way has a limit set to R 1.00. I have logged queries with Mtn east rand mall and on the customer service line approximately 7 times with no resolve. It irritates me to think that Mtn can bill what they like and customers are helpless. Mtn accounts department are asleep on the job.