Only a few organisations and people are not 'agencies'. Other rules exist to govern how they manage personal information, so the Privacy Act does not cover what they do. Organisations that aren't covered by the Privacy Act include:
Members of Parliament, when they are acting as MPs. It's up to Parliament or political parties to discipline MPs for breaches of privacy
courts and tribunals, in relation to their judicial functions. You have to challenge judicial decisions through the normal processes, such as an appeal
The news media when they are conducting their news activities. The Press Council, the Broadcasting Standards Authority and the courts govern the news media.