Most ISPs use the "abuse" account for receiving information about people who abuse the services they provide.
If you receive spam e-mail, or get hax0red by a l33t d00d, you should send an e-mail message to abuse@<insert-abuser's-isp's-domain-here>.
The action taken on receiving such a message varies from provider to provider. Some will shut down the abuser's account, send a warning, or do nothing at all.