You could disappear the bottle ones by one and explain to him that you can't buy new ones, so when they're all done, they're done! Go together to the supermarket and buy a sippy cup, and explain that this is one for daytime use, so you can't give him milk in it at night. Easy for me to say, I really do sympathise. I myself was a bottle addict, and to this day remember being 3 and throwing my last bottle in the dustbin, and the sense of losing something I had loved. (A bit like smoking my last cigarette!)

It's a vicious cycle - the more milk he drinks, the less he wants to eat, and the less he eats the hungrier he gets at night for milk. Obviously there's a psychological aspect to it too, but you will need to deal with the hunger issue at the same time.

Perhaps you could try gradually diluting the milk, which will hopefully stimulate his appetite during the day so that he will be less hungry when you start phasing out the nighttime bottles?

At 3 my (now 4 year old) son was still ADDICTED to his bottles. It was a huge headache for me, as it did not really fuss my husband. A day after he turned 3 I encouraged him to pack all his bottles into a bag for his imaginary friend. That after a whole week of prepping. We left the bag outside for them to fetch, and after bath went to fetch the bag. “They’ then left him some presents. For about a week after that he still asked for his bottles. I then reminded him of the little friends that got his bottles, and they really needed it. My now 2 year old is also HOOKED on his bottles, and oh dear, I don’t know how we are going to toss those. Luckily they sleep through, and do not ask for bottles during the night, which makes it really difficult. Especially when you are loosing sleep.
I also diluted their milk weekly, they never even noticed. By now his milk is really just cultured water. And he still loves it. It is very difficult, good luck.