Angry and Disappointed

I went to the store looking for an adapter or cable that I could use to connect my TV to the PC and was advised that I should get a VGA to RCA adapter to which I did and tried connecting it on my TV to PC and it was not working, it just gave a blank screen I checked on google for a solution and there was nothing I tried cutting my VGA cable and linked it with RCA connectors and got a blurry picture of what is on the PC. I then took the adapter back to the store and was it was swopped out and I still got the same result, I went back to the store to try and get a graphics card and I asked if Stephanie if she could refund me the money for the adapter so that I can pay only the difference and she refused and told me that she was given a written warning for swopping out the adapter the first time and I would have to resell it to someone else to which I found shocking as to how can I resell an adapter that could not work even after I tried connecting it to 3 different appliances just to make sure that the problem was not with my PC and it was not working still. I am now stuck with an adapter that I doesn't work and am wondering what are my rights as a consumer with regards to this matter