Damage that affects the screen

A computer monitor fell on my iphone x and the screen started glitching and flashing white and green till it went black so I took it to a repair shop. The screen was replaced and at first the problem didn’t go away then I took it back and after the second replacement, my phone worked perfectly for three months and then the issue came back but this time, the screen stopped flashing whenever I removed the simcard and used wifi. I used this hack till the flashes became more frequent so I took to the repair shop, this time after several visits, the flashes still more frequently over time. I’m at my wits end, what could be the issue, it seems something other than the screen is the problem.