Thinking out loud, did you believe the litter was KC registered when you bought it? Did you buy it from an advert, and if so did the advert say that it was KC registered, as if it did then you have a case under the Sale of Goods Act.
Buyers beware, there is also something called the Dog Lovers Registration Club (DLRC), which accepts dogs of any breed, and any breeding, and issues registration certificates on payment of a fee. They do not have to be purebred, and you don't even need to know who the parents were, you just pays your money and gets your certificate. A lot of people have been fooled into thinking this means they are KC registered and are upset when they realise they cannot show them or register any puppies with the KC.
However, if you are planning to show or breed then you should have at least found out about the pedigree/registration/health check status of the parents.