It appears you may have been a victim of the sort of apaling arrangements that have recently been reported in the press here:
and whilst reforms are in the pipeline there is nothing presently in place that offers full protection to exploited workers in this way:
You do have rights to pursue a claim against the employer, and perhaps as employees you should band together to do so, and I suggest you contact the Fair Work Ombudsman as a first step.
Based on what you describe it would seem there is a very good chance you would succeed in a general protection claim and be entitled to proper back pay and perhaps damages for some of the apparent breaches of the Fair work Act which your question implies must have occurred. You might also be able to claim for your travel expenses if it appears you were tricked into coming here due to their misleading you regarding the available work conditions. The problem which you may have to face is that once you leave your employment you may effectively have breached your visa conditions and you may end up being deported or having to leave earlier than you planned, but unless you intend to put up with your current situation you may just have to accept that risk.
You can read about and find the contact details for the Fair Work Ombudsman here at the end of this article discussing similarly exploited workers:
You can read about the process of initiating an action here, but be aware that for some types of claim 21 day time limits apply so you need to get on top of this material quickly.
The initial process is designed so that parties can self represent, however to ultimately force the issue, you may need to go to court and will likely need the help of a lawyer to act for you.
The cost of a lawyer may be prohibitive, but your case seems quite strong on its face and if you band together you may find some lawyer willing to work on a no win, no fee basis so that you won't have to pay much unless you succeed and only when you receive payment, though you will likely have to shop around amongst law firms to find one who will entertain such an arrangement.
Trust the above assists.
Good luck and please rate my answer.