My experience has been with getting critters on bottles: #1, they can be very picky with the formula; #2, they can be very picky with the nipple. I've actually had a doe go THREE days with absolutely nothing to eat, she was starting the downhill starvation slide; I could hear her tummy rumble, and she would always try the bottle, but immediately reject it. I finally got the bright idea to try a different formula (which thankfully I had on hand), and she immediately downed it! I've had the same thing happen over various nipples, as well--two sibblings like one, the third sibbling wanted nothing to do with it, but would take a different kind readily. Go figure!
With a calf, there's pretty much only one nipple type, unless you've been lucky enough to have others in your area (if so, buy one of each and try them all). So try getting milk on your fingers and see if he'll readily try suckling from your fingers (if so, suspect the nipple as the problem), and try offering it to him from a bucket. If neither of those approaches helps at all, try different formulas. I've had a lot of success with Dumor brand. I actually just this week had 5 kids on bottles that loved it, but I couldn't get any more, so I had to switch brands. Once they were fully on the other, they all but one began refusing it! You can also try whole cow's milk, preferably from a cow but also from the store (if from the store, try to find as close to natural as possible, like non-homogenized, minimally pasteurized--try NOT to use ULTRA pasteurized, it actually changes the protein molecules and makes it hard to digest--not making that up, had that experience with a kid, nearly killed her). You can also make an electrolyte solution with sugar, salt, and baking soda (Google it), and taste it before giving it, it should taste nicely sweet and pretty palatable. See if he'll take that. If so, it's not the nipple, but most likely your formula he doesn't want. (Consequently, taste your formulas. Some taste markedly better than others. If they taste gross to you, they'll probably taste gross to them, also, though individuals have varying tastes of course.)
Good luck! Getting a baby on a bottle can be uber frustrating, but once you finally find that sweet spot and he goes to town on it, it's SO rewarding!