My boyfriend is from Texas where this is happening (he currently lives in California, his ex in Texas) and his ex is retroactively forcing him to pay child support ($100,000) for his 17 y/o daughter she refused him access to for 13 years. His daughter's grandparents were even required by the mother, not the law, to pay hundreds of dollars to the mother before she would let them see his daughter.
When his ex finds out his daughter has contact with him, she abuses her. She physically abuses her daughter and this is in retaliation for him contacting CPS.
Family Law Attorney
Texas has a presumed limitation on the amount of back support to be paid -- it is presumed that 4 years of support is in the best interest of the child unless the mother can prove (1) the father knew or should have known he was the father of the child and (2) "sought to avoid the establishment of a support obligation. " Tex. Fam. Code sec. 154.131(d). Child support is calculated based on his income. It sounds like he needs a Texas lawyer to protect him and put together the paperwork. Look here in Avvo for a lawyer in the county where the case is filed who handles child support cases. Good luck to both of you.
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Divorce / Separation Lawyer
Child support and visitation are two separate issues. So child support is enforceable even if the parent denies access to the child. The reverse is also true, even though he doesn't pay she isn't permitted to withhold the child. Sounds like you all need to go back to court.