Worth noting a couple of things.

As the company was struck off, Andre was operating as an individual and has the liability personally.  The protections of the Corporations Act and the provisions of insolvency don't work the same.

Issuing a statutory demand (or similar) is relatively cheap, but enforcement gets expensive.  In the other case I'm running in Aus, I've spent roughly $5k on background, and an uncontested (non-court) result should come in under another $5k.  If I have to do the full court stuff, that's $20k, and I still won;t get funds back - but it will at least shut down the guy I'm dealing with.

Not being GST registered is not a flag as getting that much from a start-up exchange on the fees they were charging is unlikely.  You would only go that step if it needs to.