Regarding rent, management claims i owe from 2004, they screwed up n want me to pay?

I live in a section 8 apartment and they are constantly switching management companies, we just got a new manager and she was going thru my rent history and says she found a money order that threw her off with the total for June 2004! She sends me a 5-day notice and says I owe about a hundred dollars, so I said ok send me a copy of that Money order and I will pay it but dont send me a print out or anything hand written because anyone before her could have made a mistake. She said she doesnt keep copies, My question is, can she send me to court for not paying that money? If she can't show me any proof, how do I know if what she is telling me is in fact true? I never get a receipt that they even got the rent, they think the money order is proof of that, I say its is just MY PROOF THAT I PAID THE RENT! Arent they supposed to issue me a separate receipt? am I supposed to pay for that money of 2004?