Hardware Just bought a used 3DS. . . . . . . .

[TheZoc]

Just send them an email and tell them you wasn't aware of the ambassador program until you read in a site or heard from a friend. And, by checking the serial number on Nintendo page, it says it's an ambassador system. They will fix it for you

 

[YamiHoshi.nl]

They probably can check whether you've got logged out or not.
If they can, then it has no use.