Hi! Welcome to the Samsung Members community!
It's very difficult to find the exact size of the nano-SIM tray used. It's annoying that yours wasn't sent back. I would send another request to Samsung and explain that you're unable to contact them, or ask if they can provide any information on the specific size of the SIM tray. Online, it doesn't look too different to a regular sized nano sim tray which can be found on amazon and the likes, you can buy one online; however, I don't think it would be smart to guess and possibly jam the wrong one in.