I had a manager give me a write up for missing work. Why? Because I was in the ICU for a entire week and half after an accident. I provided every required document need for verification, including calling in to call out and my manager didn't care. I finished out the shift and then quit that day.

You should’ve contacted a lawyer after that. Thats pretty effed up and deplorable. Go for the (financial) throat to show that this is not OK to do to injured people. Either way, if it’s recent, check the statute of limitations in your country/territory. Then sue the bastard if you can. Totally illegal and you would be legally protected in that situation