Touchscreen bugged randomly without dropping it on an iPhone 5c

I have an Iphone 5c that I have had for a while now. I don’t have a case on my phone but have almost always used it with a screen protector. A few months ago I took the screen protector off as I believed it to be interfering with the touchscreen, I dropped the phone and the screen cracked and so I had to get it replaced, and get a new screen protector. I didn’t do this myself, I went to an independent shop that had repaired my phone a few times now. The phone got a new screen protector and was fine for about a month or so. Suddenly and without warning I turned it on once and the touchscreen became bugged, I tried restarting it, did a hard restart and even removed the screen protector but the problem wouldn’t go away. I can’t type some letters on the keyboard and sometimes the phone selects things without me touching the screen at all. The phone is now almost unusable. I suspect that there was a problem when installing the new screen but I don’t understand why it worked for a month without any problems, there is a strip of slightly lighter colours at the bottom of the screen that you have to angle the phone to notice, I think that this might have something to do with it. There are no cracks on the screen and there were no cracks on the screen protector. Any help?