I've recently been harassed by a very rude woman who insist I owe a grand on a loan I Co signed for in 2005. She called today to ask if I have a lawyer to be served and since I didn't she said I would be served at my employers place of work.  She says she is representing USA CHECK CASHING.
I'm contacting San Joaquin sheriff's dept today.

If you KNOW you owe no money, or believe the call was from a fake debt collector, please take the time to read this:
http://www.consumer.ftc.gov/articles/0258-fake-debt-collectors

Also, consider blocking their phone number ... google "phone blocker"

Its a collection agency called ERG. They are rude and persistent. They called regarding a payday loan collection from over 10 years ago that I don't remember. They kept calling all day. I'm still mad. They kept hanging up on me over and over again. I read that if I send a cease and desist letter they have to stop calling,  but I have to find an address first. They are fraudulent and refused to send verification in the mail.