Delete, and keep hard copy, carefully filed, of the important stuff. On your computer, keep an up-to-date index of what is in your hard-copy file. If  you use titles only, that should do. If you're really paranoid, use randomly selected titles that have NOTHING to do with the content.

Who would have guessed from title what the Manhattan Project was all about? Or that Operation Tay Bridge had to do with funeral arrangements for Queen Elizabeth, Queen Mother?

Contact the agency and ask to speak to a supervisor in regards to filing a complaint.

A breach of confidentiality and or the privacy act, contact the relevant or authority involved, if this is a serious situation resulting in the detrimental sharing or misuse of personal information I would suggest you contact the ombudsman if the information is damming or could potentially cause hardship