So the lower bolt can't be removed because the nut inside spins, correct? And you probably don't have access to the back side of the panel where the hinge is.
Best I can suggest is pry the hinge assembly up/sideways/whatever to possibly get the captive nut to grab against it's cage and enable you to unscrew the bolt. Or burn or drill the head off the bolt and deal with the damage that causes. With the hinge off, you might be able to reach inside and either replace the nut or squeeze the cage back into shape so it holds the nut secure enough to allow the bolt to be tightened.
Good luck.
