Pretty sure you have to call Nintendo to get them unlinked

Actually, through atum, your console is communicating with Nintendo's servers (you're just banned from dauth which is supposed to handle eShop content primarily). Try calling Nintendo and tell them you cannot access your console or you sold it to someone else. Also, go onto your profile from Nintendo's website and clear all linked devices with your Nintendo Account.That won't help, my console can't connect to the servers to even see if it's linked or not D: