Verry bad Service

Im a verry upset customer I bought a Samsung Galaxy J7 Pro at vodacom in the mayville mall. I had the phone for a month and the screen turned purple. I gave it in the 5th of October. Every time when i go there to find out about my phone there is a different story. I have been waiting for 3 weeks now. They send my phone back on Wednesday without fixing or replacing my phone and they said no they have to send it back again. When I got home and opened my phone the screen was even wors , were it had a small purple smudge , now its bigger and even black. Now I have to pay for a phone I dont have and my data and eveything is going to expire. And in the meantime Im without a phone.