I left work for a medical emergency, when i attempted to return to work i was denied by my employer with no reason, is that illegal?

I had a medical emergency OUTSIDE of work and needed hospital care for 3 weeks. When the accident happened, my manger visited me at the hospital and said my job was waiting for my return when I was fully recovered. Once I was recovered I tried to return to work but was denied without any reason. I am a great employee, hardworking, and respectful. get there early and stay late, always covered shifts, never called out. so I filed an unemployment claim, was accepted and claimed every week until I got a job. Now after a year, unemployment is denying my claim and wants the money back. How should I go about fighting this?