I completely understand your shock and again I am sorry. It sounds like you were very good at your job. However, even in being good at your job, an at-will contract (barring provisions to the contrary) allows your employer to terminate you at any time and for any (or no reason) without notice. As long as you were not terminated for illegal reasons or reasons against public policy
, i.e. discriminatory reasons because of your age, race, religion, gender, or national ancestry, you have little recourse. I am sorry, but unless the agreement gives you more rights than the average at-will employee, your employer owes you not duty to defend yourself or discuss your situation. Additionally, you may be terminated without a face to face. Although it is not very professional or nice, the law does not protect employees from being treated poorly on their way out of the company.
I am sorry, but given these facts, it is unlikely that you will have recourse. Even if you were to prove that your employer got the facts wrong, that is not enough because your employer can terminate you for no reason. In order to have recourse, you would need to show that either your employer violated a provision of your at-will employment agreement or that the song and dance they gave you on the way out was pretextual and that you were really fired for a discriminatory reason.
Please let me know if you have any other questions on this matter or require clarification. Otherwise please hit "ACCEPT" so I may receive credit for my efforts.