Left side mirror snapped off

My wife pulled left side mirror in before going into car wash and the folding mechanism snapped and broke; was hanging there with wire inside still intact, connected to mirror housing and still working. It appeared that the inside aluminum (or alloy?) casting broke. Little force was used, as she is a small petite woman. Dealer said not under warranty, as this is an outside moving part. I do not agree it was not under warranty, but of course we had to have it fixed to use the vehicle. Although mirror and housing were intact, were told we needed to replace entire unit. Dealer replaced it for $270 parts and $125 labor. Part number 87940-47180 described as Mirror Assy, Oute.....
I requested to have broken part back before repair was made. When I picked up car, dealer said it was in trash and they could not find it. I checked the replaced unit thoroughly and it appears they did NOT replace the plastic housing, (tape residue still there from my temporarily taping unit together to avoid it bouncing around dangling on door) but it appears I was charged for it.

I am upset it is not covered under bumper to bumper warranty; this is brand new vehicle. Also upset they charged for part(s) not changed. Can anyone suggest what course of action I have? The only person I spoke with was the Service Manager at dealership, to no avail, although all of a sudden he told me over the phone he "found the parts" and would give them to me.