Required College Payments Divorce Decree

My parents got divorced when I was about 6 months old. As part of this agreement, any part of college that is not scholarships is supposed to be split 50/50 betweeen the two. Now, recently (and by recently I mean the past 4-6 years) our relationship has ceased to exist due to large disagreements between me and the rest of his family, and him, as in nobody really talks to him anymore. I just recently graduated with my Bachelors, and today received a Bill for his payment plan saying I need to pay it. In the past, he has always taken the route where he could not pay or steal what he can in regards to me. I.e. my college savings, avoiding medical bills, etc. Now that I am a completely independent adult, can I still go after him for this? Would it be worth it? For reference, its about 2 grand, and I make enough to make it go away within 3 months or so. But I have to pay back the amount of government loans i did take soon, and this may be rough if I do so.