You can report immigration fraud by using the Crimestoppers service. Either fill in the Crimestoppers online form or call Crimestoppers on 0800 555 111.
Note: The online form link above takes you to the secure Crimestoppers web form. You and your computer are anonymous. Their call handlers read what you have sent them and will take out any information that might identify you before forwarding it to the relevant authorities in New Zealand.