Axle nut seized or cross threaded

Ok so I have noticed that my tension adjustment nuts keep coming loose on the right side of the bike. Long story short the axle is slipping backwards. I have the service manual and think no big deal it is time to adjust the belt anyway so I dive in. I can't break this thing loose for nothing using (2) 3' breaker bars what the ****? Id did move about a half a rotation now it will not budge either way. Upon closer inspection it appears to be jammed. So now it is really loose to the point that it is not rideable yet I can't tighten it or loosen the thing. The beginning threads are not crossed but there is something going on right at the edge of the nut. I have tried heat and everything. l am down to the last resort of cutting the thing off or trying to drill the threads out. Only problem is the axles are on back order from yamaha.

Any advice out there?

To top it off the socket fell off the ratchet when i stood up and put a wonderful ding/scratch in the back fender about 3/4" long. I guess there is my excuse to look at fenders from low and mean.

Can anyone help me out with this? As I am baffled at this point on how to just get this sucker apart.