Upgraded for a phone and still doesn’t have the phone

Mtn did let me know that I can upgrade. I did an upgrade online end of February, I received my phone on the 9th of March from the courier service, the phone was faulty out op package, it had a faulty pixel on the screen. I contacted the person of Mtn on the 11th of March. The Mtn shop said that they can’t take my phone in I have to arrange a pick up with the courier, after a long argument with Mtn they took in my phone on the 17th of March and on the pick up documents the delivery date to the place where the phone must be delivered was the 20th March. Since the 22nd of March I phoned to find out what is going on and how long it is going to take to replace the phone. Each time I talk to the Call Centre they direct me to a different person and no one can tell me if they received the phone, each person says that they will phone me back, but nobody calls me back with an update. No one knows where the phone is, today is the 15th of April and still no update received, but I got an invoice for the phone that I had to pay, and the amount I pay doesn’t even give me the right amount data or minutes, I get less, but I don’t even have the phone and nobody can give me any update or answer, I sent them the documents for the pick up from the Mtn shop and courier service. Nobody responded. The people aren’t helping me in any way, tell me what can I do????? I am so frustrated with this service. It is very poor and unacceptable!