Do I have a wrongful termination case?

I was recently fired from a server position in NYC. The day before I was let go my AGM asked me to stick it out with him for another month to see the improvements. That same day the GM agreed to write me a letter of recommendation for graduate school. The next morning I was fired. During the verbal firing I was told it had nothing to do with my job performance or my technical skills, but that rumor was I did not speak to a certain manager and they do not see me happy there in a month. I went to HR to get more information 4 days later; they were unaware of my termination and said they would investigate. About a week later I was told that my termination was the final decision due to my "negative attitude" that affected the staff, customers, and over all restaurant. This is not what was verbalized to me. I was never written up or officially spoken to about anything during my 11 months of employment.