MTN Problem with upgraded handset- MTN NO HELP

Good day, I am dealing with a problematic situation with MTN Midwater Middelburg Cell city ***) regarding my upgraded phone handset. The particular MTN branch where I have my contract is of no help.

I upgraded my phone on 14 Aug 2019 and received a Sony Experia 10 handset. On 22 Sept 2019 the phone handset became faulty. It displays a notice on the handset 'no service' . I took out my simcard and put it in my old handset and the handset and simcard worked. This is why i believe the phone handset is faulty. I took the handset in to MTN Midwater and spoke to Natalie. They took my phone and contacted me after a week and said the handset was fixed. I tested the handset at the branch with Natalie and it was still faulty, displaying the same message. I left my phone at the branch. I was contacted on two different occasions after that to come and fetch my handset as it was apparently fixed and the exact same thing happened, as soon as I test the handset with Natalie at the branch the handset displays the same message. Natalie phoned me after the third time and told me I have to send the handset to Boksburg Sony to get it fixed myself. I do not have a contract with Sony but rather with MTN Midwater Cell City and that is why i feel it is their responsibility to get the handset fixed or send me a new one. I am promptly paying my contract every month and for a handset that i do not have. This issue has been ongoing for more than 3 months, with alot of communication from my side towords the branch to reslove the issue but with no avail. I am out of options on how to handle the situation in a decent manner and that is why I am turning to Hello Peter for assistance as I have heard that you are remarkable in assistance with serves issues like the one I am experiencing with MTN Midwater Cell City. Please be so kind as to assist me in any way possible so that I can receive what I am paying for. Kind Regards Stella Stoberg ***