Told I owe money back on my benefits - any advice?

After 16 weeks of benefits I got a notice saying I must repay some of it. I would rather hear the honest version than the polite one. I did not notice any errors at the time. 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.

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