I appreciate the comments above about not being able to get CIO to do anything about Credit Corp - and they're right that one of CIO's board is the CEO of Credit Corp. The board is supposed to be separate, however.
This might help you get around it. You'll need to do each step in order, but feel free to skip ahead steps if you've already done any:
1. Get a copy of your credit reports from the credit reporting bodies. You're entitled to a free one every 12 months, you've recently been knocked back for credit after a search was done, or where you're requesting a correction - go here for details/instructions:
https://www.oaic.gov.au/individuals...redit-reporting/accessing-your-credit-report;
2. Complain directly to the relevant credit reporting bodies. Search on the internet for 'complaints' and the relevant body, that should get you to the right pages. The credit reporting body will then seek information from Credit Corp and make their own determination;
3. If you're not happy after 2, the credit reporting bodies are all (I think) members of the EDR schemes: CIO and FOS. Find their scheme and make a complaint. Since it's no longer about Credit Corp, for example, you should over the 'hurdle' referenced above;
4. If you're not happy after 3, make a complaint to the Office of the Australian Information Commissioner. If you get that far and no one's helped you, your only viable port of call thereafter is a court action or trying to appeal to the Minister in charge.