How am I suppose to deal with this and what are my rights?

I live in TN, my ex-husband lives in GA, he asked to have my 8 yr old son for the week, so I agreed. My son doesn't see him but once or twice a year. It states in our divorce decree that my ex only has the right to see my son if he is staying with his mother(my son's grandmother), I thought I would be nice and give him a chance on his own. Well, my son has been with him for three days now and wants to come home, he was crying on the phone to me about being hungry, his "father" being a jerk to him. Well, there was an incident today where my ex-husband told my son to do something and my son didn't want to do it and told him no. So, he calls me screaming and cursing in my ear that it's all my fault why my son is not listening to him, and now won't let me speak to him. He told me I could call between 3 and 6p. tomorrow, but I want to talk to him now, just so I know he's okay and doesn't think I'm not missing and thinking of him. I called the police in his town to go check on my son and have him call me but the police said there wasn't anyone home and to contact an attorney (which I'm going to do). I'm just trying to get some insight from other sources as well. Also, he took my son to Florida without my knowledge. He is the most hateful man I've ever met and in my opinion a bit unstable. I will never let this happen again. I'm wondering if I could go down there and get him myself and how I would go about doing so because I know he won't cooperate with me in any way. I'm just trying to find some answers before I contact an attorney. I miss my baby and feel so bad that he has to go through this, that I let this happen. Thank you for your help.