Thank you for writing. There’s an old expression, “Once burned, twice shy.” The bullying may have made him very wary about getting too close to people. It’s certainly understandable. My guess is that your son is avoiding rejection by not reaching out. But it is making him unhappy and he seems stuck.
The fact that he does go places where there are other teens shows us that he hasn’t given up. Unfortunately, he has become too passive. You say he isn’t invited places. But does he ever do any inviting? He doesn’t get texts. But does he join in the social media conversations? He needs to regain the courage he needs to actively get involved.
His unhappiness does give you some leverage to get him some help. I don’t know of any such camp. I do have my doubts that a week of coaching would solve the problem. I hope you will consider a therapist instead. I think he would benefit from on-going coaching and support. The privacy of one on one therapy may be interesting to him.
If he accepts giving therapy a try, you and his dad need to back way off. Tell him that you are absolutely there for him if he wants to talk but that you know that he has things to work out for himself.
I wish you all well,