Told I owe money back on my benefits - any advice?

I received a letter saying I was overpaid about $150 on my claim. I do not usually post, so bear with me. The letter mentions an appeal window and a repayment plan. Who should I talk to first?

I asked for a waiver and a plan in the same call, and they gave me both forms. It was less scary than I expected.

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