Get the cow in a catch and get the calf on her, or hand milk her out into a bottle to feed. I prefer to give the cows milk over milk replacer and you might be able to get her to produce more milk by simulating a calf sucking. Sounds like the cow might have to big of teats for the calf to figure it out. Keep working at it, don't give up they are resilient little critters. I had to tube the preme I have 4 times before he could stand up to get a drink. I know it's not ideal but it worked. Warm iv fluids under the skin might help warm him too? what is his temp? A little honey on your finger might give him a boost of energy and I second the vitamin B recommendation, it will help stimulate appetite.