Overpayment letter from the unemployment office - any advice?

I received a letter saying I was overpaid about $1100 on my claim. I would rather hear the honest version than the polite one. 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.

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