Adoptee how would you feel if you found out your birth mom was trying to contact you?

I gave my son up for adoption 13 yrs ago. At the time I asked for an open adoption but was adviced against it by the adoption counselor. No one helped me understand my options. I have always thought about my son and would die if I ever thought he didn't know how much I love him. I recently became so worried he might think this that I contacted his Adoptive parents and kindly asked to receive an occasional update. I told them my contact info should he want a relationship etc... They wrote back telling me he is fine and never shows signs of concern about being adopted. They said he is happy and well adjusted and doesnt need me. In short they dont want me to receive updates or contact them. I am so hurt by this. I feel like if they are this possesive of him he is probably afraid to reach out to them and talk about being adopted. I'm guessing they wont tell him I have contacted them on his behalf. Because I have no leagal rights I have no choice but to sit back wait for him to turn 18. As an adoptee would you be mad if you found out your parents withheld this kind of info from you? I'm so scared he will never try to find me cause he wont want to hurt them.