GM still has record that the VIN was run and the key code was requested and provided to that dealer though. They may not have you info but then their balls are in the sling. We used to have repo companies come in all the time for keys and without their ID, company name and the repo affidavit from the note holder, we wouldn't and according to GM were not supposed to do so.I've had a GM Dealer cut a key for me before with no proof of ownership. They kinda had an idea who I was but they had no idea I owned the truck at the time. They said they wanted to see insurance and I told them I was locked out of the truck and needed a key and they cut me one. Maybe most are more strict but it seemed easy enough for me. $50 says I could take a VIN to the same dealer off another D-Max and they'd cut me one without any proof of ownership .
I'm suprized Onstar isn't doing you any good. That's just odd IMO.