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

After 3 weeks of benefits I got a notice saying I must repay some of it. The letter mentions an appeal window and a repayment plan. Has anyone disputed one of these?

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

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