Just trying to change middle ring, 3 bolts out no problem using chainring bolt tool and allen key. The fourth one I can turn with allen key but the housing (probably not correct term) keeps spinning with it. Can get good pressure on chainring tool (not the shimano flat tool, a screwdriver style tool) but no matter how hard I apply pressure it eventually spins with the bolt and now I'm concerned that I could wear away the grooves in the housing.
So, any ideas how to undo the seemingly locked together bolt and housing?

