Anyone being contacted by NCO Financial should read this information: http://www.budhibbs.com/debtcollectorpages/nco_financial_systems.htm

And whatever you do, don't communicate with them on the phone.

Other links that may be of help:

http://www.naca.net/debt-collection-abuse/
http://www.budhibbs.com/First.htm

Another phone number used by NCO Financial.