If you have an original nut, try tapping the flat of it with a bar and hammer. I've removed a lot of them like that. It bangs up the nut, but that isn't terribly important, at least to me.
hahha not "banging my nut" either.... I would put some pen. oil on it and try it--- if you can get some heat on it that may loosen it also. Have used both these on wheel and brake parts.