I believe this may be defamation case. I was fired from my job because they stated I did not do all I could to find coverage on my shift. When I showed them the proof that I did they let me back in to work, however on the day I was fired my supervisor tol

I was fired from my job for not contacting people to cover my shift. I proved to HR that I tried to get coverage and they hired me back. My supervisor though told a co-worker and a client that I was fired for integrity issues, and once I came back to work this co worker told me what was said. I emailed HR and told them what happened and heard nothing back then 2 weeks later I was fired agin but this time for coming to work late. I believe my supervisor had something to do with this as retaliation against him. Who can I talk to about this