My question involves criminal law for the state of: Pennsylvania

I have been working at a beer store for about 5 years.A month ago, a guy from state police came in with an young man. He said "You sold beer to minor. How couldn't you find this scratch?" He showed me a young man's ID with big scratch on expiration date.
I was in a state of panic.The cop left after taken a picture of my ID. While he was writing a report, I checked CCTV. First of all, I checked the young man's ID. 20 minutes later, he came back because of license number. Suddenly he wanted to see how to cook. We said "We got to fix." He said " I'll be back tomorrow." He left. My boss and me thought that he will take a signature tomorrow. Next day, he didn't come back. 2 days later, he came back. He said "You sold beer to minor again. Sign here." I said "What are you talking about? Where is that guy? I want to see him and his ID. I got to make sure." He said "No. No. Check your CCTV. I got to protect a young man......No...No....I got to
protect my SON!!!" I asked him " What? What? Your son?" He didn't answer. He left quickly!! I got 7 letters until 10/2/15. They sent a same letter twice by certified mail.

According to the latest letter, I got to send a letter for admitting my guilty or wait for a date to be scheduled for the hearing by the Office of Administrative Law Judge.

Anyway, there wasn't district attorney's signature but cop's signature.

What should I do now? I really appreciate your advices.