ok, there is a lot of talk here about how to validate a debt with a collection agency. i'll explain how to do this with success (not guaranteed though!!).
first, once an account has been placed with a collection agency, they are required - by law - to send a written notice explaining who they are, who they are collecting for and the amount they are trying to collect. it will also include the name, address and phone/fax # for the collection agency.