Samsung Opened my Fold 5, there was a black line along the seam. Still in warranty, sent it in. They said something was wrong inside, so not covered. Internet

Fold 5 was fine, went to bed. In morning I opened my phone and a black line was running along the seam. Still in warranty, sent it in. They said not covered because it was something on the inside. Want $450 to fix.

All I did was open my phone. I did not do anything wrong. I feel they are just trying to run out the warranty (ends this month) so they don’t have to repair it.

I want to stress all I did was close the phone, then opened it in the morning. 

I contacted by phone, by chat, I spoke to the repair shop, I left a description on Samsung members community, which they deleted. I don't know where to turn to make them do the right thing.