i am a jeweler located near a kay store, and have recieved many kay customers per year oddly having the same problem.
They purchase a ring after picking it out personally , return it to be sized after gifting it , and get back a different ring but of the same style only with a noticeably lower quality diamond in it.
The troubling thing is the number of people reporting this , one person would be understandable as bad things happen and can be fixed by a jeweler making good and giving the customer a better diamond , i had to do this once actually .
However kays response on all of these unsatisfyed customers is to tell them "we do not guarantee you will get the same ring back just the same style number.
Actually to help everyone out this is against the law, once you purchase a ring it is no longer their ring it is your property. It is legal for them to do that before you purchase the ring but not after, period end of story, so it this had happened to you , your not alone and i am just one jeweler in one town, now multiply this problem by 1000. wow