I was with my ex for 14yrs we separated in 2006 custody of our children went back and forth he knew he was not our oldest childest who is now 14father but never questioned it. Our other child was adopted and is now 12, now he wants nothing to do with our oldest child so he won't have to pay child support but wants to retain 50/50 custody of our adopted child. He paid support for 6mos with no problems till I asked for a modification and it got increased by the child support services. I need help

Generally estoppel is an act or statement that prevents a person from later making claims to the contrary.

You may invoke estoppel if he has ever held himself out as the child's natural father knowing he is not.
Did he acknowledge his paternity in written?
Was the child born in your marriage?

"A line of cases holds that the conduct of a husband with no biological ties to a child may nonetheless estop the husband from avoiding parental responsibilities even after the husband’s marriage to the child’s mother is dissolved.”/In re Marriage of Freeman, supra, 45 Cal.App.4th at page 1447./



In discussing the elements of parentage by estoppel, Justice Tobriner in the Clevenger court stated that if the facts should show “that the husband represented to the boy that he was his father, that the husband intended that his representation be accepted and acted upon by the child, that the child relied upon the representation and treated the
husband as his father and gave his love and affection to him, that the child was ignorant of the true facts, we would have the foundation of the elements of estoppel.”/Clevenger v. Clevenger, supra, 189 Cal.App.2d at page 671./

We were never married he signed her birth certificate I'm aware of the cleavenger case but he hired a lawyer and they brought up arazaga case in san diego 20007 that is their argument he is saying he never knew she was not his child.