Keep trying to contact your vet, or another vet.
Heat up a hot water bottle, cover it with a towel or something to keep the kittens warm.
Go to the pet store, you can buy animal milk substitute. Make sure it is warm before you feed it.
to feed it DONT hold them like a baby. Hols them in your hand belly down. It will look strange but this is how they feed, lying the other way can cause them to choke.