How do I get my ex-husband to pay the college tuition that he owes our daughter?

The divorce decree said "Father will provide advanced funds for tuition", "Mother will pay room & board when child is home from school" & my ex would pay 1/2 of the medical insurance that my job covered. He paid 2/3 of her tuition for the 1st & 2nd term of college, 1/3 for the 3rd term. She is starting her 2nd year & he is refusing to pay anything at all because he thinks that he has "paid enough". He won't pay anything because she won't spend the weekend with him at his house which is 4 hours away. She is afraid to go because of previous verbal abuse & anger issues. She agreed to these terms & signed off on child support because she expected her dad to pay tuition. I have paid all food, medical, car insurance, cell phone etc. since the divorce. How can she make him pay what is owed?