Overpayment letter from the unemployment office after 4 years as an electrician's helper

After 25 weeks of benefits I got a notice saying I must repay some of it. I worked as an electrician's helper before this. I did not notice any errors at the time. Has anyone disputed one of these?

Read the letter for the appeal deadline and act on it, even if you think you will end up repaying. Then ask about a payment plan.