Got a denial letter for unemployment, what now? after 3 years as an insurance claims processor

I got a denial letter last week saying I left my job voluntarily, but I was let go as an insurance claims processor. I have read a lot of threads here and could not find my exact situation. 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.