Got an overpayment notice, what now? - what worked for you?

I received a letter saying I was overpaid about $500 on my claim. It has been a long 24 weeks. 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 10 months ago, and it got easier once I kept a simple log of every call and form.