Overpayment letter from the unemployment office after 5 years as a bank teller

I received a letter saying I was overpaid about $1200 on my claim. Any experience at all would help. 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 6 months ago, and it settled down once I kept a simple log of every call and form.