You don't have to call to figure out who it is. I google all numbers that come in our phone line.
When I first started sending letters, CAs came out of the woodwork. Like when I was a kid, we would throw rocks at the hornets' nest. You only have to do that once to learn.
I don't think it is extortion at all.
As a side note, back in my college days I/we owed money to everyone. The only reason I didn't owe you money is because I hadn't met you yet. I've since paid all of that off, but I learned to setup a separate phone line just for creditors. I still have a home phone, but nobody but friends and family have access to that number. Its even under a different billed name than the public line. I give everyone else the public number. It also has the ability to read off the time/date stamp so I can record the recording without worrying about taking pictures, etc. Collection calls are very very rare now, but I log each incoming call into Excel and track the number via Google.
