
Are we talking about the Kennel Club Registration certificate (equivalent to a human official birth certificate, or a Cars log book) or the Pedigree (list of ancestors). If it is the latter, you can get a 3 or five generation pedigree from the kennel club for your registered dog. Just tick the relevant box on the form when you transfer the dog into your name.
If you have no Registration and or pedigree documents then the breeder may b e a bit slapdash, or as you suspect you are being cheated, and the puppies were never registered.
Do you have the advert for the litter, and did it say Kenenl Club Registered in it. You may be able to take the matter to Trading Standards.