Violation of my RIGHTS as a consumer

I bought Defy Microwave on 27 June 2015 for R699 within a week it stopped working. I sent it back to the store for repairs. A week later it stopped working again then I did the same to book it for repairs it was fixed . 2 weeks after repairs it stopped working for the third time. Today I was at the store for the same problem and spoke to the Manager asking for refund or exchange but he refused. What must I do in cases like this please help#crying out loud#