3 weeks really isn't a long time to refuse a meal. If he has been taking 2 rats every week maybe he just isn't hungry? Did you double check all your husbandry numbers and points? What size rat is this? Is it the same size rat that he previously accepted? What type of substrate are you using? Try feeding very late at night or early morning when the room is very quiet and very dark. If its been 1 week intervals for your feeding schedule change to every 10 days. Good luck and stay in peace and not in pieces.