Horizontal/Vertical/parallel lines on screen

I had my phone sitting unused for a couple hrs then when picked up to use it had these small black horizontal lines on it and was flickering. I couldn’t use the screen properly so turned it off and when turned on an hr later it was fine, till I went to play a game on my phone and out of nowhere these big white and purple vertical lines popped up on my screen and around the edges and is really bad when I have a dark background. It also gets brighter as I’m using it. I have also noticed when I have a white background that it has very faint grey parallel lines on it. I have been told it is a software issue but what annoys me is I haven’t dropped it nor got water on it and it happened out of nowhere, but also my warranty is out. I will be looking at the consumers act as I believe this is not something that should happen to a $1500 phone in a matter of a year and a half. Has anyone else had this issue and what did you do to fix it?