Overpayment letter from the unemployment office after 12 years as a pharmacy technician

The agency says I reported earnings incorrectly, but I think I followed the instructions. It has been weighing on me all week. I did not notice any errors at the time. Who should I talk to first?

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

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