Bad Customer Service

MTN is doing its best to frustrate me on daily basis. On 14 December 2021 I went to MTN cradlestone mall to do an Upgrade. An agent by the name of Lefa assisted me. After 2 days the upgrade was not active and then I went back to the shop to check what was the problem. Lefa checked and resubmitted the request. 2 days after it was still not active. I then went back to the shop on 24 December 2021 and requested that they cancel the upgrade and migrate my number to prepaid. They again failed to migrate my number to prepaid. On the 29th of December I discovered that my number was upgraded to Sky Bronze instead of migrating me to prepaid. I then went to the shop to inform them and asked if that was not going to cause financial obligation of which they said no. They eventually migrated my number to prepaid on 02 January 2022. On 31 January Mtn deducted an amount of R953,65. I then went back to the shop to request a refund because it was their fault to upgrade me instead of migrating my number to prepaid as per my request. I escalated issue to Tshepo, the supervisor at the shop who is well aware of issue but he is doing nothing about it. I then requested that they escalate to Tshepo's manager, Karla who is also doing nothing about my request and she is not helpful. What must I do.