Reading the story, I kept wanting to say "it wasn't you that got scammed, it was the credit card company." Can the credit card companies force you to pay anything if you never actually signed or agreed to their terms and conditions?
Scams involving the mail have been around for a while. There is a reason the post office delivers a notice to your old address when mail forwarding is done.
I grew up on a rural road when people would put their mail out in the mail box and put the flag up. There were always rumors/stories of people taking mail from those mail boxes and stealing checks or whatever else. My Mother would always drop outgoing mail in town at the post office.
