Overpayment letter from the unemployment office, forklift operator here

After 18 weeks of benefits I got a notice saying I must repay some of it. There are 16 people counting on me, so I am trying to be careful. I did not notice any errors at the time. Has anyone disputed one of these?

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