Told I owe money back on my benefits - what worked for you?

I received a letter saying I was overpaid about $900 on my claim. There are 4 people counting on me, so I am trying to be careful. The letter mentions an appeal window and a repayment plan. Has anyone disputed one of these?

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.