Overpayment letter from the unemployment office after 10 years as a call-centre agent

After 2 weeks of benefits I got a notice saying I must repay some of it. I have read a lot of threads here and could not find my exact situation. 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.

Thanks for writing this out. I went through something close to it 4 months ago, and it got easier once I kept a simple log of every call and form.