Told I owe money back on my benefits, mechanic here

I received a letter saying I was overpaid about $800 on my claim. I do not usually post, so bear with me. I did not notice any errors at the time. Has anyone disputed one of these?

Thanks for writing this out. I went through something close to it 3 months ago, and it settled down once I kept a simple log of every call and form.

If you are unsure, free legal aid in your area may help for this kind of notice.