I'll confess now, I made this problem a lot worse

The nut was very stiff and rounded off with the wheel wrench so I thought I'd try and cut it off i.e. cut the sides off and knock whats left off with a screwdriver and hammer. As you can see, I've just made it worse. Tried mole grips first but got no grip. Tried a nut splitter but couldn't get the angle right.
Any suggestions pls? Cannot get any grip on it whatsoever. I guess I could use a dremel to cut the whole thing off as tight to the wheel as possible and hope the last bit is so weak I can pull the wheel off with some force. Need a new wheel bolt obviously.
Thanks
Matt