I am sorry for your pain. It is evident in your post. I think that the best thing you could do is accept who he is right now and the fact that he wants minimal contact with you. I promise you it annoys him that you call your mom to get through to him. One day in the (maybe far, mabye near) future he will realize how much he misses the unconditional love of a mother.
Stop calling him. He DOES check his e-mail, but he doesn't want to return yours. There is nothing you can do about this. He is trying to assert control over his relationship with you and you are pestering him (I say that gently. I would be hurt, too.)
My mother did this with me and I never answered her calls. Eventually our relationship was e-mail only, and only when I chose to e-mail her. She was a very difficult person to get along with, very overbearing and manipulative. I just wanted her to butt out. Also, every time we talk, even today when we are close, the first thing she does is berate me for not calling more often. I am SO sick of it that the other day I just hung up on her. I've told her for many years to stop that. Why not just be happy that I call when I do? I see her a couple times a week, there is no need for her to do that.
It also sounds like he's being spoiled rotten by your parents. What a shame. At the same time, though, you are infringing on his emotional adult space by tracking him down and guilting him. His ability to be an adult is being stifled on all fronts.
Leave him be. Stop guilting him, stop trying to get through to him. You can't. I sincerely hope that the grandfolks will cut him off, too. The kid needs a chance to grow up.