Now my child is paying for his child through the CSA – this cannot be right

my husband lost his job and cannot claim jsa as he only work 10 months and doesnt have enough stamps paid, but i work 24 hours a week and get the working tax in my name and also child tax for my 16 year old daughter who is staying in education.

Csa called us to say that i have to pay £5 a week out of my child tax for his child, my child tax is in my name and my husband is not the father of my child, i was wondering if thsi was allowed by them, as if it is then my child is now paying for his child through the csa !!! can this be right?