Hi, autistic person here.
I actually can understand what your son was going through. He was very scared and afraid. So you decided that in order to “teach him a lesson” you will keep him in this scared and afraid place. This is not a good way to help someone to deal with their anxiety. Youtube, as you said yourself, is his way to cope with the transition from school to home. What you did, technically, is taking a disability aid from a disabled person as a punishment.
Rutine is very important to autistic people. I guess you are not autistic, so you don’t see it that way, but distribution of rutine can be very painful and scary for us. I would recommend to move on to other educational tools, because probably your son don’t understand that the disruption of his rutine, and ruining his whole day, making him anxious and afraid — was a punishment for misbehaving in the morning.
I would like to recommend using different education technics that doesn’t involve rutine braking for autustics.
Please tell your son a fellow autistic from enother continent is sending him metaphorical rainbows.