What should I do with my attorney's mistake in my green card application?

I've been told by my attorney's office that my priority date for level 3 worker immigration petition is Oct 2005. They had not filed my green card application until this July when USCIS opened the cut-off date. I happened to find yesterday that my priority date was actually Dec 2004. This means that I could have filed my green card application on June and avoided this chaos going on from July. I could have saved more than $1000 because USCIS will raise all the immigration fees from July 30th, and I have to wait until next fiscal year. I also could have escaped from the current uncertainty due to USCIS's wired behavior and avoided my waiting time until the next fiscal year.

In short, the mistake by my attorney's office caused me monetary damages along with emotional stress caused by uncertainty and extra waiting time.

What should I do with this situation? Should I sue the attorney? Or is there any other action I need to take? Your advice is greatly appreciated. Thank you

You could sue for the monetary damages but no jury will award you any punitive damages. You could also call the state bar and file a complaint for malpractice. That's a blatant claim because the lawyer missed a deadline while he was representing you and that could have been completely avoided if he/she were a competant attorney.

Already taking advantage of the American justice system and your right to sue anybody anytime for any reason! All right! j/k that's pretty ligitimate

First, bring it up to your attorney.
If he won't compensate you, file a complaint with the Board and sue him.

It's so unfair and I hope you get your money back!