[geyu29]

For the first thing, not really sure with what I can feasibly say. It's obvious that DNA or "This item came in the box, but not that one" will lead to an IMEI blacklist. Don't really feel like using the return method either-- not to mention that they would be awfully stupid if they didn't check the box.

You could give reason that the item is missing and return it either way, whatever they might try to get in touch with you. They might not even contact you, after all the operation from warehouse to customer reps are different, they might have to send the information to customer reps. But you can add something else, an old smartphone maybe, or something that weighs similar? I think that would work.

But then again the item not arrived, is probably the first approach you should have, Try it, obviously they have to manually block, so make up an interesting/emotional story such as a birthday or girlfriend leaving for university lol to cause little confusion.