We have had similar circumstances since my stepson was 4. Visitation was totally denied beginning at 11. End result....the child supposedly now refuses to visit and now at age 13 has total contempt for his Dad. The court did not find CP in contempt. Does that make sense?
Instead ordered counseling, etc, which did no good as Dad was denied access by CP/stepson to counseling sessions.
End result. When a CP has money enough and is determined enough to prevent Dad from seeing child, Dad has a long battle to wage and the outlook is not good.
That is just our experience. I have not heard of much success against denial of visitation and eventual alienation of the child, especially when the child gets past age 11 or so.
Good Luck in your quest for your son. I hope it turns out okay.