I got a neatly used iphone X 2 months ago from a nairalander for 170k

I just left it till few days ago when i was ready to start using the phone

I signed in my apple ID and moved my contact and files. Face ID and all working.

I notice there is ghost touch. While using twitter, insta etc, it scrolls back or open another app. At over i thought it was screen over-sensitive but No its actually a glitch. I tried everything from forced reboot to rest settings. nothing works

This morning, i noticed its not detecting my sim also. I actually called the phone (with the owner's sim in it) before i bought it.

What can i do? Contacting d seller is a waste of time.