I think my puppy may have F.N!! (kidney failure)?

If the puppy means the world to you then make sure you get the right diagnosis from the vet. Unless you signed a contract with the breeders stating that something like this would be reimbursed, then you are probably out of luck. It would cost more in lawyer fees than if you just went ahead and paid the bill yourself - there is no guarantee you would win. Remember that puppies have small bladders and pee a lot. I had a pom puppy many years ago and I remember calling my vet about the very same thing. It turned out to be a mild bladder infection along with the fact that poms have small bladders. It eventually cleared up.