How to sue social service?

C.P.S.of social services conducted a interview, the lady went on holiday vacation but before leaving told the assumed father NOT to have any contact what so ever with my 2year old granddaughter.The day before she returned his attorney had a herring that the judge even tho he is a convicted sex offender and under new investigation for sex crimes gave him 50/50 with him having the child more custody. No one from Social services showed up in court to represent the 2 year old. After she returned, she stated that he refused to contact her. Him and his mother took the child to Children` s hospital to have her examined making false statements of sexual abuse.The court ordered 50/50 on medical decisions yet they lied at hospital stating father had sole custody.His mother stated that there was blood in dipper yet gave child bath before taking her to hospital E.R. There was Not enough evidence for police to file a case and doctor even stated that it unable to state abuse had even taken place. Cps had father move from mothers stopped visitation from mother seeing her at all. Child's grandmother has custody even tho state does not allow that, But CPS treatments to put child in foster home, and states that I must take polygraph test that police refuse to give because no charges- refuses to let mother see child till test is given testing cost 6 to 900.00, I am on disability, all statements by father against me police have contacted and know there lies. Father claims to have DNA from before baby borne yet even tho court and CPS have been told that it is one he forged will NOT CHECK IT. I have never had any sex charges- he is a convicted and under new investigation-police took over 3,000.00 of his P.C`s that are being gone through by police & FBI. yet CPS refuses to pay for testing and holds my granddaughter hostage- it would take 1/2 to 90% of my check making it impossible to pay rent/by dippers and things for child food stamps does not cover.