I have seen those channels twisted like a piece of decorative wrought iron furniture from someone twisting and twisting.
Sometimes you need to bite the bullet and cut a neat hole in the inside of the door with a cut off wheel to get to your work easier. With that hole, you can grab ahold of the channel to apply more force to the bolt. You will need to weld the cut out piece back in once your done. When you replace the bolt, do yourself or the next guy a favor and use a stainless steel bolt with anti-seize on it.
Carl
