It is commonly misunderstood that child contact and child maintenance are linked, and a parent who is refused contact with their child may consider that they do not need to pay child maintenance for a child they are not able to see.
Equally, if a parent is not paying child maintenance that they are liable to pay, the parent with whom the children live may feel that they should have less contact with the child on the basis they are refusing to pay.
Under the law of England and Wales, if you are liable to pay child maintenance, this liability remains even if you cannot see your child.
Child support payments are deducted from universal credit anyway.
They may have an informal arrangement and the woman has decided not to pursue a claim for spousal maintenance (if they were married).
Mind your own business, why do you want a family living precariously to be worse off because of jealousy, own sense of righteousness or whatever it is?