I had that happen once on another device. I wound up putting a screen protector on over the mark, which made it invisible. Obviously it was still there underneath, but I couldn’t see it. Maybe that would work for you.
I would be very upset as well. For this device, I an using a little microfiber cloth that I lay on the keypad before I close screen.
I do the microfiber trick because I like to have one with me and this is a nice secondary effect. Never had a problem with it falling out - the case closes too tightly for that to happen.