Got a denial letter for unemployment, what now? (Pittsburgh)

I got a denial letter last week saying I left my job voluntarily, but I was let go as a bank teller. Thank you in advance. My employer's version of events does not match mine, and I have emails that show it. Did you bring documents or only talk?

File the appeal before the deadline, even if you are unsure. You can gather documents afterwards. That is the one part I would not wait on.