Got a denial letter for unemployment, what now? - what worked for you?

I got a denial letter last week saying I left my job voluntarily, but I was let go as a payroll clerk. This is my first time dealing with any of this. My employer's version of events does not match mine, and I have emails that show it. If you have appealed before, what helped you prepare?

Legal aid offices and some workforce centres help with unemployment hearings at no cost. A call is worth it.