Coilover insert nut is stuck

[luca]

So I've got different top hats to install on my AJPS coilovers but I've run into a problem.

The nut that holds the damper, top hat and camber top together wont undo without the insert spinning, and nothing I've tried has been able to hold the insert still including vice grips, multi grips, impact wrench etc.

The setup is AJPS coilovers, techno toy tuning camber plate.

The pic is just to show what's happening, although I jack the suspension up through the shock tower hole when I'm trying to undo it.

I'm running out of ideas on how to undo it so if anyone has any ideas just let me know!

Thanks.