As a first step, you should get in touch with the organisation in question and ask them to stop sending you mail.
Organisations are often allowed to use information that is publicly available − for example, they can use contact details they’ve found in a public phone book – so this may explain how they obtained your information in most cases.
However, it may raise issues under the Privacy Act if another agency disclosed your information to them, if they didn’t have a proper basis for doing so.
You may want to consider signing up to the Do Not Call or Do Not Mail service run by the Marketing Association as a way of decreasing unwanted mail.
If you received the mail by email, fax or text, you may also want to consider contacting the Department of Internal Affairs, as it is the agency which enforces New Zealand’s anti-spam law.
Learn more at privacy.org.nz