I have recently been in the same position. I came over on. 457 visa in November, from the beginning, I wasn't being paid on time or properly, and having days unpaid even when I was working. I wasn't paid any superannuation and it was clear the company couldn't afford me. I was given a pay cut to just $800 a week before tax (with no written warning)which when I pointed out was a breach of visa conditions I was told that I had to hand my notice in but first request 4 weeks unpaid leave. The company led me to believe that this was in my favour to increase the time I had to look for another job. I refused to hand in my notice so was made redundant that day. They wouldn't pay me any notice period as they said the wage cut was notice of my redundancy. I had to wait 4 weeks for any annual leave entitlement to be paid to me. I now have another job and a nomination has been submitted, however immigration have said it may take up to 3 months to process. I am desperate to work I haven't worked for 6 weeks, I have next to no money and no way of earning any.
To add to the irony the company I was with re advertised my role and recruited on a part time basis, they also have never told immigration that I have been maderedundant and when I ask immigration about this and make complaints I am told nothing can be done. The 457 was definitely a huge mistake for me I do wish I had gone down the PR route to begin with.