In his executive summary,Ombudsman Phil Clarke said issues including misclassification and under-reporting were identified in the investigation.
One of the most glaring issues highlighted in the report was that the department's Complaint Management System does not comply with the law.
"The internal review mechanism provided under the department's complaints management policy and procedure does not accord with the Australian/New Zealand Standard because it does not provide for a merits review of a previous complaint process or decision,"the report stated.
In layman's terms,the system does not comply with the industry standard,which is required by law.
The report also declared the complaint system was"unnecessarily complex and confusing"and leads to"frustration and delay".
"Decision-making in the management of complaints was a key concern identified in the investigation,"according to the report.
"A lack of clarity about how a decision about a complaint should be made and who should be the decision-maker has resulted in poor outcomes for complainants."