being accused of abuse

more to add to the long saga.stbx left after 23 year 3 children 17 14 11.he took the youngest boy in feb and refused to return him and applied for cro which is still ongoing.
he was supposed to take the oldest boy but that lasted a week and he has now returned home.
he constantly played mindgames with the youngest 2 and eventually took the youngest and undermines my authority at every turn.their behaviour is appaling and they threaten me and are abusive and if i try to say anything they ring their dad.he has removed my daughter twice from the house against the court order and i can do nothing.
last night she asked to go to her dads tomorrow but we all ready had plans so i said no.she went ballistic shouting and screaming at me and the next thing i know she has phoned her dad and said that i had grabbed her by the throat and tried to strangle her which i hadnt.
she is much bigger that me and i hadnt touched her.he then ran me and said he was going to phone the police and tell them what i had done ane remove her from the house which i said i wouldnt agree to.
he spent 30 minutes on the phone being abusive and then rang me back and said she could stay but he will tell the court what i have done and take her.
i am really afraid of what she is going to do next as i have no way of proving that i dont abuse her and am scared that social services might get involved and my children put in care .this is breaking my heart that they have no love or respect for me and are willing to make up all these stories.
i am scared to be on my own with her now in case she says i have done something to her.dontunderstand how he can get them to act this way.her behaviour is vile and it feels he has left her here to take his place.please help me has anyone had a situation like this and do i just let her live with him but he will twist them and i will loose them forever:S