My ex-husband does not communicate with me or help support his child because he thinks I want his money.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

A father is obliged to bear, to the extent of his capacity, the necessary expenditure such as food, clothes, accommodation medicine and the like, of his poor son before he reaches the age of puberty.  This ruling does not change whether the father is still married to the child's mother or has divorced her.

If the child becomes pubescent then his father is no longer responsible to spend on him except if he does not have sufficient income to fulfill his necessities.  If the father does not pay the expenditure of his son then you may demand and take it from him in a court of law.

Allah knows best.