Can you be fired while on disability?

I was on disability a little over a month. When released to return to work I emailed my employer letting them know I'd be ready to return to work the following Monday, after not recieving a response for 5 days I text my boss letting him know i had emailed him but hadnt heard back and i was released and ready to start Monday (it was a friday). He text back saying "Call me Monday for details." I called Monday and he said that they no longer needed my helpas he hired someone because he could not wait for my return anymore. I adked him to send me an exit letter but he never did.