I had the same issue with my Samsung S5 phone, and it turned out that the Micro SD card was the problem. I too had given up, and started looking for a replacement. I decided to copy the contents of the Micro SD card so that I could transfer the data to the new phone. When I removed the card, I noticed that the phone was functioning normally. I also received an error message when I inserted the SD card into my computer, that the SD card had errors that needed fixed. I fixed the errors, copied the files to the hard drive on my computer, and then re-formatted the SD card, and my phone is like new. The screen no longer flickers. This appears to be a fairly common problem with the Samsung phones that use Micro SD cards. My first suggestion is to remove the card if you have one, since it may be the cause of your flickering screen.