Told I owe money back on my benefits after 15 years as an IT help-desk technician

After 19 weeks of benefits I got a notice saying I must repay some of it. Thank you in advance. The letter mentions an appeal window and a repayment plan. Who should I talk to first?

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