Ghost Touch on iPhone X

Hi,

So about 4 months ago I bought an iPhone X in Malta from an unauthorised reseller, and I also bought a case specifically for my iPhone in order to protect it. Now what I have noticed is that my iPhone is experiencing an issue known as 'Ghost Touch' where the screen just randomly swipes and enters apps by itself without me touching it. Now the reseller told me that I will need a screen replacement which is not covered by the warranty.

Should I ask for a full refund? As I am starting to think that the phone is defective and it has nothing to do with the case that I bought it.

Thanks