How can the CSA find my ex?

May 30, 2015

I got 2 disable children with my ex.he has stoped paying me money for them because his mother say the kids are not his but we had dna test on the kids to prove the kids are his.

Csa say they can not find him with his national insurances number. they have visted him but no luck.

I not allowed near him due to him beating me up. please can anyone help how i can track him down.