Imac 27" 2017 Failure

I have an IMAC 27" 5K display 3.8GHZ 15 which is only 3 years old. When the IMAC was only 1 or 2 years old, I had issues with the screen going dim and which became more prevalent over time. I also have the "backlight stage" effect where it looks like there are torches shining from the bottom of the screen upwards. This problem occured to the macbook pros and Apple had to repair the units at their own expense after a class action was brought against them. Apple is refusing to acknowledge that they have sold a faulty computer to me. If you have had the same experience, please share, so Apple can be held accountable. I have conducted some research and come across other people experiencing this problem. Apple's repair service provider have quoted for a new display screen costing around R13500. I dont see how such a new computer should need a diplsay replacement. I have an 11 year old Mac which has a perfect screen.