How do I get my son out of foster care after he was taken away from his mother

[William36]

 My son is 5 years old and the mother has custody.  She has kept me from seeing him as the parenting provisions state that parenting time is flexible upon her discretion and with her present or a third party agreed upon being present.  I live 150 miles away and she will not agree to meet me half way.  I have tried numerous times to try to see my son and she either moves or changes her phone number. I just found out that she had all of her 4 kids taken from her home and placed in a foster home.  I have been in contact with FOC and the foster care facility that my son has been placed in.  I am having problems getting information as they think I have no parental rights.  I want to get my son out of there and get custody of him.  He has been out of her home since January.  I'm not sure what to do next and what my rights are as far as getting my son from the foster care facility.