Besides all the nice advice that others have added, I'll give you mine: talk to a lawyer, and have him send physical letters to the company, and to YC.

The lawyer gives you two things:

1) He knows if you can be compensated for the damage;

2) It would give YC an opportunity to take care of this matter.

Oh, and by the way: I don't know their side of the story, therefore I don't want to judge; however, it is very likely that they lied to you - letting someone go after two weeks is weird, and I don't believe that "it's not about you".