Sinotec 55" HD TV

We bought our TV from Makro Amanzimtoti in December 2016. In August 2017 we had to take the TV back to Makro Amanzimtoti as it had sound but no picture. It took 21 days before we got our repaired TV back. Today (3 February 2018) we have had to take the TV back to Makro again for a second time as it again it has sound but no picture. We have been informed by the manager that unfortunately we cannot get a refund as the TV has to go for assessment, once again. I find this utterly ridiculous. The TV has a 5 year warranty but has had to be returned twice now within just over a years time. This product is clearly faulty as while I was there another customer had come to check if their 55" Sinotec TV was back yet after being returned two weeks ago for having sound but no picture. Their TV had been purchased only 5 months ago... All I want is my money back. R6999.00 is not a small amount and I'd like to buy another TV as soon as possible!!