Overpayment letter from the unemployment office - first time posting

I received a letter saying I was overpaid about $1050 on my claim. Any experience at all would help. I did not notice any errors at the time. Who should I talk to first?

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 8 months ago, and it got easier once I kept a simple log of every call and form.