Why are they doing an internal investigation over my termination?

I was notified via phone call that "We are going to find out were you really are in the disciplinary process and we will get back to you with the results." Prior to the mentioned phone call I was fired and it was not a nice letter. It made me sound like I was a crimnal. I applied for unemployment benifits and furnished a 6 page paper along with 14 pages of documentation clearly proving I was falsey accused. I was awarded benifits. 4 days after unemployemnt recevied this information is when I received the phone call. My termination letter stated that I triggered the final disciplary action by being late on the 18th which lead to your termination as well as I violated a work rule class b "no call no show" on the dates of the 15th and 16th which results in termination. Let me add I was hired to only work weekends. The dates mentioned above were classes held in the middle of the week which I called the day prior and stated I did not have child care for my 3 year old. The class was held over 1 and 1/2 hrs away at a sister facility. I have documentation to note they did not comply with their attendance policy and violated FLSA by not acknowledging travel time as work time. Instead of compensating me in pay they wrote me up for leaving early and arriving late. I transported a employee for the benefit of the company for compliance with state guidelines and was not my normal route I take to work. The employee I transported lives over one and a half hr away from me and under my direct supervisor I was told to do the above. They altered my time sheets on more that one occasion, accused me falsely of things I did not do and retaliated by taking the house keys off of me in front of the entire staff on the 1st floor nurses station. It was assumed I had my own personal key when I sure did not. I was being watched by one single person who's intention was the outcome-termination! With this said, I have documented proof that I did not in excess accumulate tardies, leave early and absences to warrant termination. I have signed time slips and pay stubs to prove that I was approved for the majority of the accused dates yhevwritten warnings note. I grievance everyone to to my direct supervisor with no response noted. I went by chain of command to his boss who then terminated me while this the grievance was taking place. Ther is alot more but I get so upset and anxiety filled I geet pain in my back to the point I can not sit stand or walk, I am wonder if I was wrongfully discharged. I do not want to waste my time and nervous system because I was an employee at will; however I feel harrased, intimated, and discriminated. I am white and the person behind this mess is not. The only issue that I ever had was the above which all has to do with time and schedule as the scheduler is not white. I AM IN NEED OF ADVISE THANK YOU