Your son's name is not unusual.
I've been a teacher for over 40 years. In many ways, the schools have their hands tied by policies, but you do have to give them a chance and they can't change what they don't know about.
I'd start with the Head of Year or similar position at your son's school. Make sure they know you're not messing around, you will take things further if need be. Now, sometimes, as a teacher, I know I might as well be talking to a wall with some bullies, but hearing that a parent is prepared to take things further does get through to some kids. Let the teacher know that you'd like them to share with the students that this will go further.
If it happens again, lets say they stop for a couple of days, but it starts again, then take it higher. Again, let them know that you're not going away quietly, this will go further.
I've seen horrendous bullying brushed under the carpet by some school leaders. They don't want to suspend students as it is reflected in data for the school. Higher up, some see suspensions as a sign of weakness in a school, whereas I see it as a sign that a school won't put up with bad behaviour.
The squeaky wheel gets the oil, please squeak as loudly as you need to for your son. As I said, classroom teachers can only take things so far, consequences for really appalling behaviour often have to be given the okay from above.
I always tell kids they are lucky that more parents don't go straight to the police, as their behaviour is considered as assault on the other side of the school fence.
I have seen incidents where parents went to the police (yay) and it did have the desired effect, it also had an effect on some of the fringe dwellers, who didn't want to end up in that sort of trouble. Hopefully you won't have to go that far, but bullies can be sneaky, do things as soon as adult backs are turned. If you do end up having to go to the top, just know, that secretly, plenty of teachers will be cheering you on. Unfortunately, they can't publicly go against the actions of the school, but they agree with you.