Told I owe money back on my benefits - what worked for you?

After 8 weeks of benefits I got a notice saying I must repay some of it. The letter mentions an appeal window and a repayment plan. Has anyone disputed one of these?

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

If you are unsure, free legal aid in your area may help for this kind of notice.