AFAIK if you bought it in SK then you can only purchase AppleCare for SK. Do you have a Korean address? Is your Apple ID account set to Korea? You might need both of those to be true. Whatever the case I’m pretty sure changing your billing method back to USA is not the solution.
AFAIK if you bought it in SK then you can only purchase AppleCare for SK. Do you have a Korean address? Is your Apple ID account set to Korea? You might need both of those to be true. Whatever the case I’m pretty sure changing your billing method back to USA is not the solution.