Can I file a discrimination against my previous employer?

I had worked at dunkin Donut for 4 yrs. I was wrongful terminated without a reason. I told the manager n the owner that I can not work Wednesday afternoon n willing to switch with Tuesday afternoon. The reason is that I need to study for my graduation exam. A week later after my written request, I went to my workplace make sure they did not schedule me until next month. I noticed my name was taken away. Normally my name would still be there without the time. One month later I went to look at my schedule my name wasn't there. I wrote a note to the manager n the owner asking why my name is not there. They never called me. I called couple of times left them a voice messages but never get to me. I am tired of how they treated me because I am Chinese. I had been working in different position for them including shift manager, donuts finishing, baker and overnight with same old salary. I did not receive the equal employee training and benefits. What information I need to provide?