I was on a leave of absence over the summer and apparently the leave did not properly go through and was told a month into the summer. They told me they needed more information so I handed in another form with the same information as the first. Well during this time they ended it without me knowing and scheduled me without knowing. Now I am trying to come back and I was told they were going to fire me. I was a really good worker before I left, how can I defend myself here?
In addition, they said they called me but they did not and I was still listed as LOA on the schedule.

-I will also have a union rep with me.

It's a good thing your a union employee. I'm not sure the union rules in your union. Have the form that has you listed as loa. If you were listed as loa then why did they schedule you? If you're loa was due to a medical condition make sure you have your doctor's notes. You could try to say something about the phone calls but that would be your word against their word. Also you said you were a good worker prove it. Good luck and listen to your union rep