uniform gift to minors act

My grandparents passed away in the late 80's, at which time i was still a minor. I am an only child--as was my mother. My mom claimed her parents (my grandparents) had no valid will, and everything was left to her. My grandparents had a considerable amount of money, and they let me know that there was some supposed to be for me before they died. It was always her word against mine. Recently, I came across some bank books that were set up for me by my granparents under the uniform gift to minors act. My mom withdrew the money after my grandfathers death, and it has never been paid to me. What can I do now?