Told I owe money back on my benefits - 13 months and counting

The agency says I reported earnings incorrectly, but I think I followed the instructions. I did not notice any errors at the time. Who should I talk to first?

Keep everything in writing and save the confirmation numbers. It saved me later.

Thanks for writing this out. I went through something close to it 13 months ago, and it got easier once I kept a simple log of every call and form.