My ex never looks after our son and we’ve never had any money

I have a 3 year old and I’ve not been with his dad for about a year now and when I ask for some money to support his own child he always turns round and says no or when he does its only like £10 every time he feels like it he never helped me out through the pregnancy or even after he was born, he earns about £250 a week, he never has him.