What do I say about why I left my last job?, payroll clerk here

I have an interview next week and I am unsure how to explain why I left my last job as a payroll clerk. I would rather hear the honest version than the polite one. I have been practising in the mirror.

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

Keep everything in writing and save the confirmation numbers. It saved me later.