Told I owe money back on my benefits (update)

I received a letter saying I was overpaid about $500 on my claim. I would rather hear the honest version than the polite one. 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.

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.