Ex-wife horror

I've been married to my husband for almost a year. We have been together for over 3. His ex wife has never liked me. Mt step children and I get along for the most part. I am very close to the two middle children. The oldest girl tells me that she hates her mom and does not want to go back home when our weekend is over. She has told me that her mother and mother's new bf use drugs and that she has found bags (zip lock bags) in her room and lots of money. Anyhow----We had the children for the month of July and all was well until My husband's ex wife, Beatrice, calls and wants me to get off of work early to meet her so I can drop off the children. When I told her "no" she got up set and cussed me out and hung up. Well, she never came to pick up the children when she was supposed to (07/31). I even sent her a certified letter letting her know that we had moved and giving her our new numbers a week before she was supposed to get the children. My husband and I called the police to file a report because she thinks that she can call my work place and leave me threatening messages and talking to my supervisor and try to get me fired. When we talked to the police on 07/31 my step daughter told the officer that her mother abuses her and using drugs and sells them. The officer called a crisis counselor who turned around and called CPS who turned around and opened an investigation on her...Yesterday, 08/03, I get a call from a clerk who works in the family court. He tells me that Beatrice is in his office saying that we will not give the children back to her (I can hear her crying and carring on). I told the clerk that she is lying and gave him the police report numbers and CPS report number. I get into an arrgument with him because he is saying that Beatrice did not get my letter, which is a lie because I have the ticket showing that she signed for it...Long story short....My husband finally talked ot her after 3 years of silence..she cried to him saying that I was coming between them and that the kids hate me and that I was the cause for all of this. I DO NOT know what to do anymore. I have tried to be nice to her and talk like adults for the kids. My step daughter DOES NOT like her and refuses to go back. We do not want to let her go back, but she keeps on harrassing me at work. I have tried to ge the Police involved but they act like they can not do anything. i have changed my cell phone number 3 times and still she gets it...I am at my wits end and fear for myself and two other children. What can I do?????