Told I owe money back on my benefits - first time posting

After 3 weeks of benefits I got a notice saying I must repay some of it. I have been trying to stay organised about it. I did not notice any errors at the time. Who should I talk to first?

Keep everything in writing and save the confirmation numbers. It saved me later.

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