Why is my dad treating me like this?

Ok so my dad said if I pass my Bio Regents (a state test) he would give me a computer game he bought me. Well I passed with an 81, but he refuses to give me the game or to talk to me. I did fail the Geometry and History Regents but that's not what he promised me. Our promise was that if I pass BIO I will get the game, not if I pass all my regents. Why is he treating me like this? He broke his promise. It's not my fault he didn't say all regents, he specifically said BIO. Please no rude/immature comments.. I'm not in the mood right now.