[Solved] Please help CSA tribunal ruling!

Please can someone help me to point out where it says in law when the CSA payments stop when a child receives income support for themselves and child benefit stops. We have lost our appeal because there is no legislation that supports our case to stop child support Maintenance being paid when my daughter has a child of her own and she is a parent with care for her own daughter. Child benefit is exempt and had to be paid back by my ex wife. My daughter claims income support , child tax credits and care to learn for her own daughter and my ex wife earns more than I do and is exempt from claiming child benefit. My ex wife takes rent from my daughter and her income is too high to claim any benefits. I have my son living with me and a residence order, but my daughter lives at home with her mother, we are divorced over 9 years ago and my wife kept and lived in the house which she sold less than a year later for a clear profit of £90,000. We had an agreement in court where I paid child support to her, but 12 months later she went to the CSA and was paid less money through them, but it has been financially crippling. I paid CSA payments for both children up until my son came to live with me four years ago. We are struggling financially as my new wife's health has suffered and has not been able to work, the only benefit we do claim is child benefit for my son. The tribunal has just ruled that there is nothing in child support legislation to support our case regarding any rules relating to the child being in receipt of income support precludes an award of child support as my daughter is studying Asa levels at college and still 18 years old the judge ruled that she is still a qualifying child for the purposes of child support agency. There is no child benefit anymore for my daughter but the CSA have ruled I still have to pay the CSA payments, even though my daughter is supported by her own benefits. The web page on gov.uk and hmrc we pages state that CSA payments stop when a child claims income support for themselves. Please does anyone know where we can find a legal document in legislation that supports this? We would be happy to support my daughter directly but the mother is taking the daughters benefits from her as rent and this seems greedy and unfair to my daughter when my ex wife's income is over seventy thousand pounds and would not qualify to receive benefits. We are stuck in a legal loophole and it also looks like there is possible benefit fraud going on. In the meantime we have one month to appeal, but cannot find the legislation to support our case. We have provided all the legislation to show there is no qualifying child. But the CSA state that they have applied the section 55 rules of the child support act 1991 and child support maintenance regulations procedure regulations 1992 and that it does not matter that child benefit is not in receipt to the mother and the child is a qualifying child is still in approved non advanced education and under 20 living in the home of the mother. But surely this would open the flood gates to all the teenage daughters who are themselves mothers and a parent with care to claim thousands of pounds in benefits when they live with their mother who is a high income earner. Isn't this defeating the point of giving benefits to those who genuinely need them. We cannot afford a solicitor and tried for nearly a year to fight this at appeal, but this was the result. Please can anyone help?Thank you 😮