Told I owe money back on my benefits after 16 years as a mechanic

I received a letter saying I was overpaid about $750 on my claim. It has been a long 15 weeks. I cannot afford to repay it all at once. Who should I talk to first?

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