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

I received a letter saying I was overpaid about $1000 on my claim. Thank you in advance. I did not notice any errors at the time. Who should I talk to first?

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

Collect your pay stubs and certification records for the weeks they name. Mine showed the error was a date mix-up.