CSA – quick to demand, slow to resolve

My partners daughter was kicked out by her mum so i claimed benefits i rung the csa who said i couldnt make a claim for csa until i was in receipt of child benefit so i waited as soon as i had it i contacted them who inturn contacted the parent who said that the daughter 17 yr old was moving back in with her and she did

1 week later we got a letter from csa demand finance info it totally threw me as i had to be getting child benefit before i could claim i rung them they closed my case but it took 4 weeks to sort out benefits the 17 yr old hardly goes to college when living at her mums beats me how they can ask for our details so quick when they cannot prove she is getting child benefit