Overpayment letter from the unemployment office

After 12 weeks of benefits I got a notice saying I must repay some of it. This is my first time dealing with any of this. I did not notice any errors at the time. Has anyone disputed one of these?

Keep everything in writing and save the confirmation numbers. It saved me later.

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