Hearing toll not paid

Hello I’m a student and have the truck driver’s license, because I can help drive a truck. I drove with a 12 t truck and a 10 t tandem trailer. Normal is the toll machine always on, because the trailer is always there, but this time it was off and I did not notice it or checked it. The boss also never says we should save toll or something similar, the colleagues also often drive with a 7.5t truck solo to pay toll, because they do not want to turn it off. Now I am at the Autoba hnauffahrt Altmühltal drove to the A9 and the BAG pulled me out at Kindinger Berg, up in the parking lot. The official of the BAG said, since there would be only 2,xx € that I did not pay will come true nothing. But last week there was a hearing, at which I have to speak. What should I write in this now best. Some have already said, I should not pay afu no case, because it is not going to court because of 2,xx €, but I believe too hot. W he high would be the penalty for me and how high would be for the vehicle owner? How is it the usual who pays the penalties? best thanks