MTN Billing post service cancellation request

I upgraded my cell contract to a data bundle. At the time of the change, I asked the MTN representative to check and cancel any recurring data bundles that I may have subscribed to as I would no longer need it. The representative checked and said there wasn't any. I kept on being billed for a weekly data subscription though, so I went back to MTN on 4 occasions to check. They couldn't find this weekly data bundle on my MTN app, or on their system so logged queries. This took months to resolve. MTN (Fourways) said that they'll request a refund as the service couldn't be cancelled by either myself or by them. At some point MTN helped me to make the billing spent 0 so that the service couldn't go off. The service was eventually stopped but now MTN refuses the refund. This is not acceptable at all. I was at the MTN branch on numerous occasions. Latest Ref: ***