Help!

My fiance and I have had full legal and sole custody of my step son since 2005 and last summer my step son's very unstable birth mother filed for a change of custody. The judge denied it but after about 6 months we stopped getting any mail from the court and it turned out the clerk was mailing everything to my fiance's address from 05. ON what the judge thought was our forth time blowing off court she gave my son's birth mother custody. She has open neglect cases with DCF and multiple 51 A's for neglect that she has received in just the last month alone from all mandated reporters. We found out that the court was using the wrong address and tried to tell the judge but she didn't care. She actually removed our son from us and we have no DCF at all, no neglect issues, no drug use, we don't even drink! We have a nice home and my fiance has a great job. We also have a wonderful 5 year old at home. The judge ended up removing my step son from his birth mother but placed him with my father in law. I don't understand why she is doing this!? Once she was informed that we did not miss court she said that we should have put our son into counseling and because we didn't it was neglect!!! That is not neglect and she has overstepped her boundaries! My fiances ex has convinced her she's the victim even though she's the one with the violent past and domestics against my fiance and my son. She has so many neglect cases and charges pending, why is this judge doing this? My son is so messed up now because of this. He hates his birth mother and he has a right to after everything she has done to him. She lies and manipulates everyone she meets. What the hell do we do now? My son is gonna be 13, I'm his mom not her! She never cared to be there before but she see's a built in babysitter in my son as well as more food stamps and she thinks shes gonna get child support even though she has never given us a dime! She has had the police called on her twice with my son there in the last month, and she let him walk a mile all alone through the woods to get to the homeless shelter she lives at and when he got there she was in a hotel across the street. Than she lied to the cop and gave him this big story about how she had to chase after him screaming his name but said she never took her eyes off of him. The cop told her she should come up with a better story because if that was true he would have been there. Than when they went to get her ID the cop found her infant daughter asleep on a couch with the door propped open completely alone. Remember, she was seen walking from a hotel across the street about 20 min before they went to get her ID and the cops, my son and his grandfather were outside for 45 minutes before she came out. That means her baby was alone for over an hour that we know about. My son has become angry and quite and he snaps at everything now. No matter how many times he tells his birth mother that he doesn't want to live with her she refuses to listen. He even told her that she's ruining his life and she doesn't care. He doesn't call her mom he calls her Robyn. He calls me mom. I've been the one to raise him, give him advice on girls, help him with homework, buy his clothes, cut his hair and all those other good things that Moms get to do! Not her! She wanted to use drugs and party not be a mom. She's still using and refuses to do right by her kids. What do I do now?