Told I owe money back on my benefits, office manager here

I received a letter saying I was overpaid about $100 on my claim. I have been trying to stay organised about it. The letter mentions an appeal window and a repayment plan. Who should I talk to first?

Thanks for writing this out. I went through something close to it 14 months ago, and it settled down once I kept a simple log of every call and form.