Balls go off feed for many reasons...I have many that are off food now...After all it is the breeding season......As Tracy Barker says....A happy healthy ball python will eat when he's hungry....also I noticed you said your snake was 1200+grams, and ate 3 mice when you fed him...a snake that size will easily eat a small rat....If rats don't work....just keep offering food weekly....he will eventually come around...I actually had an adult male ball go off food for 8 months....then one day he started eating again....

Hope this helps..
Justin McBrayer