Why does my phone keep clicking things itself?

My phone is currently nearly impossible to use, my OLD phone was water damaged, and I sent it in after being sent this refurbished unit. the phone walked great for the first almost moth but now it is acting like there is someone pressing random things on the screen. I have no idea what could have caused it and have tried everything I can find online, and have even factory reset the phone. also this issue is still there but not as bad if I use the S-Pen. I have no Idea what is wrong or what to do at this point, other than try taking it in somewhere, but I cant really afford that at the moment. Someone, please help!!!!

EDIT: it is working again, after I let it sit for 20-60 minutes. But this problem keeps coming and going, if anyone has any idea what is wrong that would still be greatly appreciated. I’m wondering if I may have gotten an improperly refurbished phone.