Denied unemployment, how do I appeal? (San Diego)

I got a denial letter last week saying I left my job voluntarily, but I was let go as an insurance claims processor. It has been weighing on me all week. My employer's version of events does not match mine, and I have emails that show it.

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

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.