Told I owe money back on my benefits (update)

I received a letter saying I was overpaid about $600 on my claim. This is my first time dealing with any of this. I cannot afford to repay it all at once. 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.

Thanks for writing this out. I went through something close to it 2 months ago, and it got easier once I kept a simple log of every call and form.