Can I sue previous employment for wrongful termination; reinstated; denied med loa ext.&unemploymen

I am seriously considering suiting my former employer for wrongful termination they claim to be accidental months later; reinstated me then screwed with me ever since I got sick and went on medical leave of absence. 6 mos paid and 6 mos unpaid due to seriousness of illness. 3 mos before my full year is up the employer denied my MED LOA extension for the final 3 months. Waited 4 days to tell me this and told me that I voluntarily terminated myself. I filed for unemployment against them and was denied due to the fact that they said I quit. My union rep has not returned calls or emails. Do I have a chance of winning against them? I have all documentation in Writing from both sides.