What can be done on the denial of parental rights by custodial parent?

I am living in Texas and my children are in Arizona with the custodial parent. Recently my children 13 and 15 informed me that their stepfather had been hitting them and it has been happening for some time. They stated he mostly hits them across the head and back. I contacted CPS and it is in the process of being investigated. Now my ex-wife refuses to allow the children to have any communication with me. She has threaten them of removal of their computers/cell phones if they contact me. She has been logging on to their Facebook accounts and has been posting negative allegations about me so that family and friends view the comments. What can I do? My children are my priority by I feel helpless that I am in a different state. What actions can I take?