HEAVENSWARD Pre-order: Question about regions

[Cartry]

Thank you for taking a look at my post.

My SE account is of NA region because when I made the account (2007ish for FFXI) I used an American address. I have since moved to the UK but I think still play on an NA version of the game (I bought the physical game in Hong Kong where they sell the NA version) and all my outgoing payments seem to still be in USD (automatically buys currency and converts it but it still says it's charging me in USD rather than Pounds). I have sought help before in changing regions to EU but to no avail.

My current question is: do I buy the American edition (USD charged) Heavensward preorder or do I have to buy the EU version because my billing address is now EU. And if I buy the EU version, will the EU edition be compatible with my current game.

Thank you,

Cartry