His job made him take off the whole 2 weeks that the doctor wrote on the form.
That was the correct thing for them to do. And that sounds like about the last thing they did correctly.

Two actions he should take.

Appeal the UI disqualification https://www.tn.gov/workforce/unemplo...-decision.html

Look into taking action via the DOL or a lawsuit for an FMLA violation. https://webapps.dol.gov/elaws/whd/fmla/13.aspx