I purchased the expansion on the battle.net app, and the price really was oddly high, it also prompted a subscription window which I clicked off because I thought I am already subscribed. I then realized the purchase went to my EU account, which is inactive, instead of my NA account.
Is a refund possible?
I would appreciate any help as to under which section I should open a ticket.
You can see if the self-service refund option will work for you first off. If it doesn’t let you, it will then offer you the chance to make a proper ticket about it. Now, you may have to change the US to EU in the link, but this should be the path for you:
https://us.battle.net/support/en/help/wf/wow/1151/1152/submitted
Now, they will have to refund it back to you and then you can turn around and purchase the proper region. They won’t let you swap it out real time, just as a bit of a heads up for expectation’s sake.
Many thanks!
I was indeed able to refund the purchase.
A note to all: Please watch which version of the website you are purchasing on 
I do not recall seeing a selection option this time around in the PC App store,
and will try to purchase again on the correct region.
It happens quite often, I’m afraid. But glad it was a easy fix for you! ^^ (and for any who trip over this at a later time, you can swap out the US for EU and it will still get you to the refund service).
Update: If you are purchasing through the PC app and want to make sure you are in the right region, select the account option below the product image on the right panel and you will be prompted to switch store versions depending on region.
In general, take your time when making purchases to review all the little options and print
anyone could clearly see I made this post, and surmise I also made the purchase with great haste and hype!
Looking forward to the WorldSoul Saga and beyond!