Under at will employment doctrine, employees can be fired with or without reasons except for illegal reasons. As such, there's not much you can do to get the job back unless the employer contracted to employ you for certain period of time and broke the contract or the termination was based on illegal reasons.
However, if they cannot tell you what rule you broke and you don't know which rule you violated, it seems that you may still be eligible for unemployment benefit.
Talk to an attorney to better evaluate your case. I cannot give you any advice based on the limited.facts provided here.