What is the ruling of Islam on a woman's customary "khulʿ" divorce in order to continue receiving child support, despite the father's demand for his daughter? Is that considered forbidden, and how should the father act according to Sharia?

If the mother remarries, her right to custody and maintenance is forfeited, based on the Prophet's (PBUH) saying: "You have more right to him as long as you do not marry." Any deception to obtain maintenance is considered consuming people's wealth unlawfully. The father has the right to refuse to pay maintenance and to file a lawsuit to prove her marriage and her disqualification from custody.