Got an overpayment notice, what now? - first time posting

I received a letter saying I was overpaid about $800 on my claim. I have read a lot of threads here and could not find my exact situation. 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.