Overpayment letter from the unemployment office after 9 years as a web developer

I received a letter saying I was overpaid about $650 on my claim. It has been a long 12 weeks. The letter mentions an appeal window and a repayment plan. Has anyone disputed one of these?

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.