Was a wrongfully terminated? And can my exemployer really sue me?

I was fired last week my employer told me it was because no one on the crew liked me and he was tired of the drama. Also he told me I was fired because my wife was talking on Facebook about how I never get hours and no one on my crew wants to work. I did not even know about the comments but it did not say anything about the company or the names of the company nor my boss yet he threatened to sue me for defamation of character over something I had no clue about and when nothing in the comment was even defamation of character I do not see how he could sue me for it. I needed a termination letter for Dhs to prove I no longer work there. I received the letter in the mail today only it said I was fired for excessive tardiness over 45 times, cell phone use, and degrading company online. I know I was not tardy that many times, nor have I been tardy in over a month. I was never given a warning, the only write up I ever received while working there was the one time I called in when I was really sick and did not have a doctors note. The cell phone use, I never used the phone unless we were doing nothing or I was driving to and from job sites and I used my Bluetooth. I never talked on the phone while actually working since the new handbook came out that said we were no longer allowed to. Again I was never given a warning about using my cell phones either as again I did not use it while working so never needed a warning as to why I am confused as to why it says that was one of the reasons I was fired. And the degrading of the company again was not me and my wife was not degrading the company by saying we were not getting hours and no one on my crew wanted to work. What can I do? I was told something completely different and I did nothing wrong. Since I have no warnings at all would the reasons on the letter be considered wrongful termination?? And can he really threaten to sue me over something that I did not say but my wife, and is her saying that actually degrading the company?? Please help!