???Can someone repossess a dog i bought?

I just bought a dog from someone who bought the dog from a breeder...apparently the people i bought the dog from breeched their contract with the breeder. I have all the papers to the dog. the people i bought the dog from gave the breeders my info and now they are calling me saying they want the dog and its their dog. is this correct? do i have any rights to the dog? can they come take him? and also should i make a contract saying that the ownership is signed over to me from the people i bought the dog from? THANKS so much...i know its confusing but i really need legal advice on this.