But seriously, try some penetrating oil or else I found some crap called freeze-off. Its a penetrating oil that also cools/freezes the oil that comes out so it will help to cause some expansion/contraction between the stud/nut and get some oil in.
I had to remove the nut off mine the other day and it almost seemed like it was melted to the stud. It took some of my impact gun, while holding a screw driver behind the bracket to get it to come lose. Just be careful, that plastic isn't very strong. Like Ttocs said, penetrating oil.
Yup was able to finally get it. Torquing it before twisted the distribution plate in the bottom of the fuse box and pulled some of it pins and bent them, figured out that's why my power seat and CIG lighter quit working. Was able to disassemble the fuse box as much as possible and was able to hit it with an impact while able to get good leverage on the stud and plate.