The box is loose (recessing), and I can't keep the box forward enough to insert the receptacle (GFCI) and mount it to the box. I know about H-Clamps, but they keep the box from fall out of the wall. My problem is that the box moves back into the wall.
Post a picture and some more info.
Is it a reguler wood framed building, block walls, steel framing,
Is it drywall, plaster, paneling on the walls?
The box should have had two flanges, one at the top and one on the bottom to stop it from falling into the wall, is there no flange or has the material where they would sit been damaged?