Welcome
You are doing the right thing.
They may be right though, they may not be, but the important thing is you are doing the right thing.
When dealing with addiction, all you can do is "the next right thing" and then let go of the outcome.
A few things I have learned, is to not go to a "dry well" when it has proven repeatedly to be dry. Those two are a dry well. The next thing I have learned is to go find someone with exact experience in what it is I am dealing with. There are Alanon and Naranon meetings with decidedly "parental" slants, as opposed to spousal. maybe try to find one of those?
The next is, teen sobriety is growing by leaps and bounds where I am from. There are "sober" schools, teen meetings, teen support, it's growing in leaps and bounds.
The standard "formula" I hear is the first "rehab" rarely "takes" but it plants a seed, a period of sobriety tends to mess with ones drinking/drug use and actually cause it to escalate as it "rebounds" which results in a "bottom" which results in sobriety.
I've seen hundreds of examples of this with my own eyes.
While your child is under 18 the way I see it is when you are responsible for him, rehabs, sober schools, everything you can do to educate him and interfere with his drinking and drug use is "your job".
Rehabs (and raising a child) in many ways are like Boot Camp, people telling you things you don't like and don't understand in order to keep you alive after you leave.
Your job is keep flinging stuff against the wall to help your son, just remember you aren't in charge of adhesion.
Hopefully something will "stick" for him
just remember it won't necessarily be on your schedule.
My prayers to both of you.