Employer asked me to leave work due to covid like symptoms then terminated me due to job abandonment. How can I fight this?

I was off sick with covid like symptoms for several days.  I tested negative and returned to work the next day with a doctors note. My boss heard me cough and requested me to leave. Stated he wasn't comfortable with me working even though I had a negative test. He did not give any direction on when I could return and I did not get his request in writing. This was on a Friday. Monday I emailed the HR lady requesting a copy of the covid policy. She asked for me to be more specific. I explained the events and how my boss asked me to leave work Friday and I did not know when I could return. Did I have to wait till my cough was gone? Did I need to retest? What was the policy? She responded at the end of day with a few more questions. Also stating they follow cdc guidelines and timelines are important. That I should respond promptly to avoid further time off and so she can advise me how to deal with my situation and provide me with a return to work date. I got all the details together. Provided dates and attached my doctor note. The next email I received from her stated that I failed to inform my boss of my absences since Friday and they are considering it as job abandonment and therefore terminating my employment.  What just happened? Can anyone help me understand this.  What can I do? I live in Wisconsin.