if it was me I'd probably call whatever # you find for the airport and try to dial through the voicetree by hitting 0, #0, *0, or something like that.

ask to speak to the mgr on duty.

briefly explain your situation, without getting abusive, and ask for name and contact info for their area mgr.
they might not want to give that up, but be stubborn as hell on getting that info.

also, go to their twitter feed, and possibly facebook, and state your complaint.
they hate twitter complaints.

generally speaking, I would strongly advise anyone readIng this to either get a receipt and scrutinize it, or go to hertz.com shortly after and use your driver's license # to pull the receipt up --- DO NOT TRUST HERTZ TO DO ANYTHING!