selling me a defective Sony M4 and not fixing it

I went to vodacom twice. To get my upgrade<br> I had to wait about an hour and a half each time. To find out that they did not have stock the first time but I can complete the paper work which will benefit me when I picked it up. When I went to pick it up none of the paper work I did previously saved so I had to start all over. Only to receive a defective phone. My phone came back from repairs today and it still does not work. Now what?!