Today is one of the few days I get to sleep in past 5 a.m. (I have work at 6) so I usually turn the ringer off on the phone so no one wakes me up. We have call notes where people can leave a message if we miss the call. My dad checked the call notes this afternoon and sure enough, Bay Area Credit had called and left a message telling him to call back.
He did, and for the first time encountered a polite CSR who asked my dad some questions - What number was dad calling from, did he reside at a certain address, did he have a certain phone number. It turns out that the address they thought dad resided at was one he and my mother had lived at for a couple of years in the early 80s after they were married. They moved into the house we are currently at when I was born, so someone else was already living at the prior address in 1986 when they were saying my dad didn't pay a bill. It seems that either there is someone with my father's name or similar enough to it living at the old address now, or somehow they got address and phone numbers mixed up because when the CSR asked dad if he had a certain phone number, it was just like ours except off two digits at the end. I asked my father if they'd ever had that phone number, and he said no that when they moved he had our phone number transferred so the one two digits off has never been ours.
I want to thank everyone for the wonderful advice they gave me. :) My dad did look at the links and read up on the laws and how he could protect himself. Luckily, it looks like he won't have to send a letter telling them to cease the harassment. No letter explaining the debt has arrived here but I wonder if one was sent to the old address. Probably not. The CSR apologized for bothering my dad and said that he had entered the new information into the computer - so no bad service from that guy, just from his asshole coworkers that were so rude and aggressive they didn't even try to figure things out like he did. Hopefully since they now know that my dad doesn't live at the old address they'll stop calling because otherwise they *are* going to get a letter and he's going to file complaints because clearly they are harassing the wrong person for that old bill.