Well, that sucks. Not surprising Nissan wants nothing to do with it. They aren't known for owning up to their mistakes, let alone fixing them.
Again, given how half-assed their "repair" procedure is, IMO you're better off doing it yourself anyway. Cut out the rotten area, cut a patch panel to fit into the hole, then butt weld it in there, followed by seam sealer, primer, and undercoat. Just slapping a patch over the rotten metal leaves a cavity that'll collect more dirt and moisture and keep the party going. I'm guessing you want this to be a permanent fix, not a band-aid. Probably a good idea to drape a welder's blanket or wet towel or something over the CV axle so you don't burn holes in your CV boots. Also obviously make sure there isn't a wiring harness, fuel line, brake line, etc on the other side of the metal before you cut and weld, that could make for a bad day.
Given that it's structural, if you aren't sure of your welding skills or the best way to go about this, talk to a welder or a body shop and see how they'd tackle it.