Repaired phone given to someone else...still waiting 7 weeks later

On the 30th of March 2019 I took my Samsung A6 Plus to MTN President Hyper, Krugersdorp for repairs because it was giving me problems on charging system and the picking up of network. I was assured by the the Mtn assistant that I will get my phone back after 21 days. I got a call to come and pick up my phone on the 29th of April, way after the 21 day period. The service assistant gave me a phone, and when I checked it was not mine, he did not even check the serial numbers before he gave me the phone. When I told him the phone was not mine that’s when he checked it and confirmed it was not mine. He checked only to find out that my phone had been delivered to Mtn at Protea Mall. I offered to go and pick it up from Protea, but he said the phone had been already sent back to Samsung so I was supposed to again wait for a call from them. They did not call me until the 4 th of May. I went to the store and I was again given a wrong phone. I requested to see the branch manager and he promised to make a follow up and told me he will call on Wednesday the 8th. I never received a call, I went back to the store and they informed me that the phone was again delivered to Protea Mall and it had been picked up by another customer. They said they were trying to contact the customer to bring back the phone but the customer was refusing. They said they will block / blacklist the phone. I informed them I no longer want that phone because it has been used by someone for a long time. But up to now I have not received any feedback from the Mtn Branch. I am paying the monthly installments for the phone that I am not using and my data is expiring because I am not using a smart phone currently. This has been a great inconvenience to me. I have lost faith in Mtn especially the President Hyper crew. I have been a loyal customer of Mtn since 2012, never missed a payment but I have received very poor service from Mtn. The other scary issue is my phone had all my banking details and I am afraid the person who was given the phone might abuse some of my private and banking information.