When you buy a KC registered pedigree puppy you should get the KC registration certificate plus a pedigree (which is just the dog's family tree). The breeder can only register the litter if both parents are registered with the KC and are obviously both purebred specimens of the same breed.
What you can do about this depends on how the dog was advertised. If as you say you have proof it was advertised as a KC registered puppy then you might have a case against the breeder under the Trade Descriptions Act, and also the local council might be interested as if they have more than four litters in a twelve month period they have to be licensed.
From what I know however, unless you have the registration certificate this breeder would probably claim you knew that the puppy you actually took was not pedigree, either because you changed your mind about the one advertised, or that it had already been sold, so it would be your word against his. If you do have the registration then the Kennel Club should be informed, and they would advise you how to proceed.
Unfortunately this sort of scam happens far too often, which is why I always recommend people to get a puppy through contacting a breed club secretary who will recommend reputable breeders who belong to their club.
One thing though, you do realise that the cost of a 'labradoodle' is far higher than a pedigree labrador or poodle! Often sold for around �800 - �1000.