FFS no wonder you're fuming
Unfortunately I know nothing about the law in the US, but I would think that with a temp job they can fire you whenever they like. I would go and get legal advice about them lying about you to the agency, but unfortunately I would see it as being their word against yours,and if they're willing to lie like that, they've probably got a couple of staff members who will back up the lie.
I am really sorry to hear about this, it really does fucking suck.
How did your conversation with the agency go? Did they seem to believe you?