sky need to reset your address on your existing card. had this problem with my fathers when we tried to register for BT sport on Sky. When that's done, BT should be able to match your sky card address to the BT account address. Not sure how long it will take, as we never bothered... Found his new card in the drawer (mother had packed it away!), he forgot he had one!
ps...doesnt effect sky viewing, just linking of bt addresses with sky addresses for bt sports viewing.