Nintendo Will still unlink your Nintendo network ID from an old 3DS that you no longer have in the United States.

I had to call in and speak to two different supervisors and beg them, but the second supervisor escalated my ticket and was able to get it unlinked. they asked me the typical questions like birthdate and some of the games that were purchased on the account, but I was able to get it done.

I was also able to log into a used 3DS that I bought off of eBay and redownload software off of the eshop. I had no idea they stopped offering the service for unlinking a Nintendo network ID when I bought the 3DS used, and I'm really glad I was able to get it unlinked because that was a $300 brick at that point lol.

good luck and don't give up if you need to get your Nintendo network ID linked!