Overpayment letter from the unemployment office - what worked for you?

I received a letter saying I was overpaid about $1050 on my claim. I have read a lot of threads here and could not find my exact situation. I did not notice any errors at the time. Has anyone disputed one of these?

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

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