Mtn south africa just dont respond

I have upgraded on phone in nov 2019 still havent recived my phone, i have been calling them every week at firts they take 2hours to pick up then they reply by saying they will come back. Package has been send in dec did not receive it. So now they send my a bill to pay but how can i pay for something i havent recieved. They keep on telling me they will come back to me