Is the calf turned out with other cows and their calves? If so its possible that the calf is 'stealing' milk from the other cows. If this is the only calf, and no other cows around, then pent the little bugger up. In about a day this guy should be good and hungry. Back his little butt into a corner, and straddle it with your legs in front of its shoulders like a head-catch. Pry the mouth open using the fingers of one hand and stick the bottle in the mouth with the other hand. Squeeze the mouth around the nipple a few times to get some of the milk dribbling out. Stroke the throat as well. Eventually the little guy will catch on. It WILL get hungry. Be sure it has access to water. This calf can be fed a bottle.
I have rodeo'd around with calves older than this and got them to take a bottle. Sometimes it just takes longer with some calves.
Good luck.
Katherine