Told I owe money back on my benefits - 11 months and counting

After 9 weeks of benefits I got a notice saying I must repay some of it. Any experience at all would help. The letter mentions an appeal window and a repayment plan. Are payment plans possible?

Thanks for writing this out. I went through something close to it 11 months ago, and it got easier once I kept a simple log of every call and form.