MTN and Summer Mobile - Pathetic Customer Service

I was contacted during the month of April 2019 by a representative from Summer Mobile, with regards to a pending upgrade. The representative claimed to be calling from MTN ( at this point i did not know anything about Summer Mobile). I subsequently went through with the upgrade, and an Iphone XR was delivered to me during May 2019. However, the handset was defective (reached high temperatures during normal operations), and I was requested to drop off the Tableview MTN store. This was done on the 29 May (the handset was handed over to Llewellyn Sanders at the store. Only then as I informed that I had to deal with Summer Mobile directly, and not MTN. This came as surprise to me. I have emailed Summer Mobile numerous times for an update, as of today (23 July, almost 2 months later, neither Summer Mobile nor MTN can tell me where my handset is ???

- What is Summer Mobile's affiliation with MTN ? - Why are employees from Summer Mobile representing themselves as MTN representatives? - Where is my handset and when can i expect a replacement ?