I think the worst thing about this is Emirates lack of support once they'd offloaded you (for no fault of your own).

They should have at least put you up in a hotel (I believe there is a transit hotel within Changi?).

You may even be due compensation due to Involuntary Denied Boarding, but I think Emirates would be very forceful in opposing this.

As mentioned upthread, if you having already returned, check that your returns tickets have not already been cancelled due to you not showing for the Singapore-Brisbane leg. I doubt this will have happened though, as your flight was Dubai-Brisbane - which you actually showed for.