Maisie8

So I need to replace the rear license plate on my 1995 Subaru Legacy Sedan. When I go to turn the two bottom screws the just turn forever without moving out. I figured out that the plastic backing that the screws go into is not connected or not catching onto the inside of the car (in the trunk). I tried cutting them off, forcing them to pull out (rocked the whole car but they didn't move), and pulling while unscrewing. I can't get them off. I was thinking that if I could be inside the trunk and hold the plastic backing that I could turn the screw, but I can't seem to get inside. There are holes inside the trunk where I can see behind the plate where the plastic backing is, but I can't reach them and as far as I can tell I can't take anything off to get to them. Any ideas??