Got an overpayment notice, what now?

After 23 weeks of benefits I got a notice saying I must repay some of it. I would rather hear the honest version than the polite one. I cannot afford to repay it all at once. Has anyone disputed one of these?

Thanks for writing this out. I went through something close to it 7 months ago, and it got easier once I kept a simple log of every call and form.