Quit job, found out was underpaid...

I was working for a company and ended up quitting because I moved town. Anyway I have just found out 2 months later that I was being underpaid at that company and I feel like I was used.. I am wondering if there is anything I can do about it? I live in Australia..

Might be you can file a dispute with the local bureau of labor, or the Australian organization that essentially files complaints on the behalf of workers who have been unjustly treated. Years ago, I worked at a non profit organization in the US and helped many people with employment issues, some similar to this.

At least once a week, I had to file paperwork with the government on their behalf regarding businesses that had treated the people, my clients, unfairly. Hopefully you can get the paperwork done & get the business to own up to their mistake. Good luck.