Well, they likely have this info down on your account now, so they probably won't be coming off their decision. Too bad.
I don't know what you can do at this point. I know I have seen a number of users complain about dust under screen on here, but we're not ATT, so they would likely never agree that it is a known issue because of posts from here.
My advice: quit carrying it on your pocket. Lots of lint in there.
If you can't get this one replaced or a decent other phone, just clean this one well, and get it out of your pocket.