It sounds like that must have been a difficult operation due to one or both testicles being retained inside the abdominal cavity and having to be surgically removed. Did anybody at the vet's mention that would be the case? Was it an expensive neuter? It sounds like it was horribly botched. You could probably sue the vet but certainly you need to take your dog to a different vet and see if it needs a second surgery to fix it up. Get a recommendation from a local for a different vet!