Told I owe money back on my benefits

After 16 weeks of benefits I got a notice saying I must repay some of it. Any experience at all would help. I did not notice any errors at the time. Has anyone disputed one of these?

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 11 months ago, and it settled down once I kept a simple log of every call and form.