Told I owe money back on my benefits

After 19 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?

Collect your pay stubs and certification records for the weeks they name. Mine showed the error was a date mix-up.

Thanks for writing this out. I went through something close to it 14 months ago, and it settled down once I kept a simple log of every call and form.