Overpayment letter from the unemployment office - what worked for you?

I received a letter saying I was overpaid about $650 on my claim. I am in Cincinnati, in case local advice matters. I did not notice any errors at the time. Has anyone disputed one of these?

If you are unsure, free legal aid in your area may help for this kind of notice.

Thanks for writing this out. I went through something close to it 8 months ago, and it got easier once I kept a simple log of every call and form.