First night i recieved incorrect 20 digit code. Second night i double checked all squeenix account info was set to NA, was logged into my account.

Then i simply re-entered 18 digit code, took me directly through with no error this time to a page with a 20 digit code in NA, i just followed hyperlink on that page and finished it up from there. Try starting over with your 18 digit code and see if that doesnt give you a new 20 digit NA code