http://www.ftc.gov/os/statutes/fdcpa/fdcpact.shtm
Sample dispute letter: http://nedap.org/resources/documents/DisputeLetterwithElectr...
Sample "cease contact" letter: http://nedap.org/resources/documents/CeaseLetterwithElectron...
It's actually a pretty nice, common sense law. Note that if you intend to dispute the charge, you should move quickly: there's a 30 day limit from first notice.
http://www.ftc.gov/os/statutes/fdcpa/fdcpact.shtm