Got an overpayment notice, what now? after 12 years as a nurse's aide

I received a letter saying I was overpaid about $950 on my claim. I would rather hear the honest version than the polite one. I did not notice any errors at the time. 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.