I believe I was targeted for termination. Is that practice illegal?

I was on a 6 month corrective action for time and attendance. I was chronically late, but my attendance was fine. I corrected my tardiness completely. Had not been late since my verbal warning, however, I was ill , and called out sick 03/13, 05/24 and 08/13. I had a doctors excuse for 08/13. My leaders said Piedmont Healthcare did not recognize a doctors excuse as valid. I told my leaders that I was going to file a grievance. I week later I was sent home for a bogus dress code violation. 3 days later I was fired over the phone by a HR person with my leaders on a conference. They never sent me a separation notice. When I went to the unemployment office to file my claim, I found out the reason they gave the Ga DOL, was inappropriate actions towards a supervisor and they said that I failed to do my job. I can prove neither is true.