Why wouldn't a car dealership have a bill of sale to give me?

I hold power of attorney for a relative and sold her luxury car back to the dealership she bought it from -- they paid me, the check cleared, they said they'd return the plates, and when they sent me the check, I thought the bill of sale would be included, but it wasn't. The guy I sold it back to, who was wonderful throughout the entire transaction, was suddenly hard to get in touch with, would return a phone call but not leave a message, then I finally sent a firm email and the reply was they didn't exactly have a bill of sale, but he'd put something together for me, and that was a week ago and nothing. I've only traded in cars, never sold one before, and as POA, I need a bill of sale, what's going on here that I'm missing, it's a well known and reputable dealership. Thanks for any help.