What would I have to do,or who would I contact if a detective was trying to blackmail me?

My ex wifes father is a city official. He works for the water sewer maintence, also orginizes events for the Faternal Order of Police. He's friends with judges,cops,and detectives. He has a vendeta out for me. I am a recovering addict. There for he had Child protectives services involved and bagered and harrased us to the point that the kids were removed and forced us to place them in his gardianship. he then held it over his daughters head and gave the altumatom of divorcing me or she would never see her kids. He had a detective make it nearly impossible and scare his daughter into beliving she would never have her kids with me around and that he would make sure of it. I had a record of domestice violence. He told her that if she didnt tell the judge I hit here she wopuld go to jail. Two years pass. We got back together then I was clean four 45 days. Pryor to this my ex was clean and got our kids back and tehn her mother die witch forced her into relapes. The he called CPS again and they were monertering the house closely. We got back together because I was Clean. My ex has problems with depression and pain she has the on goings of cancer in her female parts. She there for was prescribed what she was for depression and pain and it was aprooved by Cps. He had suspected we were high called cps. Let them in the house called his cop buddies,said she was incompasited while I was sleeping in another room. Then the cops hand cuffed me and threatend to get me with another domestic. They took her to the hospital and her dad petitoned her into a mental hospital, he told the doctors she abused Prescribtion medicine,Cocaine and Iv drugs. They can never find a vain in her to draw blood or anything when she goes to the hospital so they had to put an Iv in her neck! Now if she was shooting dope she would have some tracks or vains for that matter, Her toxicology report came back negitave and her family doctor was well aware of what he prescribed her. After being at the hospital I left and Acidently hit a curb. Her father and his detective friend tryed to set me up he came to my house witch the father owns and told me that he was going to prosecute me on all these bunck charges if I did nopt leave her alone he threatend me again and I just dont know what to do. He told me if I just left her alone my problems would fade away/ What should I do Its so much more deeper then this?