Need Advice: Might Need to Sue former Bosses. But before I do...

[bettyellen]

I was laid off the Monday of Thanksgiving week in New York City.
During the termination conversation, my bosses said they would take care of me, I said in addition to serverance, I had not been able to take most of my earned vacation this year.
I received a paycheck to day not covering that Monday at all. I had already corrected the HR person and reminded her I worked that day. I also corrected her statement that I had taken all my vacation. They owe me eight days. I did not receive a response. The problem is, they didn't pay me all three weeks vacation for my first year there, either. They didn't allow me to take it, and then said I didn't take it quickly enough and never compensated me for it. Their employee handbook says one week, but three weeks vacation was part of my salary negotiations. I had already a 7 year history with these people. I think now they are going to pretend I was never given three weeks.
A year ago, I had talked about leaving the company and they gave me a big lecture about how I owed them the chance to work things out, they would never dump me like that, etc. I actually turned down job offers because I thought I had job security at least. So I think there's some basis for misrepresentation there.
I need to try and reach the more reasonable two of the bosses on Monday and see if they will be more reasonable, but it seems like they have been hiding from me.
I am afraid if I cash this check, I am stuck without getting paid for that Monday if I cash it Is that right?
The big problem, I am probably going to have to threaten to file a complaint or sue them. And I have nothing in writing and two partners willing to lie about anything to anybody.
They didn't even pay me for the last day I worked there, which flips me out so, I am ready to get a lawyer. But is it a big waste of time?
Are they going to take any threat seriously knowing I have nothing in writing?