Game Store Robbing People

I bought a television at Game in Vredenburg it was showing a fine line on its screen although it is a brand new T.v then I took it back to them they tested it and they saw the line that I am talking about and then the Line Manager phoned the Technicians explaining to them about this line,they asked me to wait for 21 day so that they can figure out what is the actual problem with it.After 5 days on their 21 days waiting period they called me telling me that my television is cracked inside the screen and I must pay R6500 to change the screen although I bought it with R8000.I asked them how could I pay the television although it is still on the warranty.I told them that if the problem is inside the Television that is not my problem I bought it like that which means its a factory fault because I am not the first customer complaining about this problem.They say they not going to help me I can do what ever I want to do I feel like I am being ****** because they still have my Television and my money as well.I always buy from them and I have the other appliances that still on warranty so I dont know what is gonna happen if one of my appliances gives me a problem the way they treated me now.I need help or advice please