grandma

I have permanet coustody of my grandson since he was 1 year old, he is noe 7, 3 months ago i made a verbal agrement with his father to see if he would get use to living with him, but so happens that my grandson now wants to come back and today i went to pick him up and the dad which happens to be my son, would not let me take him, the police was called out and i showed them the legal papers and they told me that since i got the papers from the courts in New York that i would have to get one from the courts down here in florida, this does not make any sense, the paper is legal, i need to know what i can do to get him back.