It's easy to make a mistake and set the wrong kind of eggs. I have a friend that has both silkies and Call ducks, and she one time sent a silkie egg to a customer with an order of Call duck eggs because they are the same size and look similar. A similar thing might have happened here, if you ordered these eggs or if they're from your own birds and you also have ducks or peafowl, or guineas, since guineas can also take 28 days to hatch.