Ring came out diamond within 5 days of purchase

My boyfriend wanted to buy me an engagement ring on 05/10/2015 he made me choose which ring I like and I did. I was told the ring I want has one diamond missing and they said the rings are finished. I then went to another jewellery store, but couldnt find what I wanted. So I went back to American Swiss to my suprise they found the exact ring I wanted. My boyfriend and I were very much suprised cause earlier they told us that they were finished but now they are available. He asked to see the 1st ring which we saw was missing a diamond we saw it. So he paid for the second ring. And put it on my finger. Today on the 09/10/2015 my ring came out one diamond after 5 days of purchase. How possible is that? <br> RING DESCRIPTION (***) CLASSIC RINGS the sales lady is MANAMELA NTHABISENG