Hisense's terrible service

About 3 weeks ago I upgraded my MTN contract and got myself the Hisense H50S 5G. The phone worked fine for the first week and then suddenly started giving problems with signal. I couldn't make or receive any calls as I also never had any signal. I went to MTN to complain, thinking it might be a network error on their side. It was then that a Hisense rep told me that there is a faulty batch of the H50S' doing the rounds and that they are aware of the issue with the phone. He told me to backup my phone and bring it in so they can replace it with a new phone. It has been almost 2 weeks now and I still don't have a new phone and I still haven't been contacted by the Hisense consultant. I went back to MTN to find out what is happening and they claim that they are also struggling to get hold of the Hisense sales rep and there is nothing they can do to help me until the sales rep makes contact. So for now I am having to pay for a phone that I don't have and don't know when I will eventually get the new phone.