Tyler was taking the exact same amount of formula when we started him on whole milk at 11.5 mo. Before that, he only used the sippy cup to, well, sip. He'd have maybe a sip or 2 and that was it. I randomly picked a bottle (lunch) and stopped offering it cold turkey. I gave him solids with a 6 oz sippy of milk instead. I offered the sippy periodically during the day so he could take a sip here and there. I waited a few days for his appetite to adjust then dropped another bottle. After about 1 month, 3 of his 4 bottles were gone (we waited a couple more months to drop the bedtime bottle for other reasons). He wasn't drinking near enough milk yet, so we made up for it with other dairy products like yogurt and cheese. He gradually got used to it and started guzzling milk like there was no tomorrow!
Some people will mix the formula and milk and gradually reduce the amount of formula in the sippy if their LO refuses to have anything to do with it. Oh, one more thing, the 24 oz per day guideline includes all dairy products, so you're right...24 oz plus cheese and yogurt is too much!