THX Promo code for 50% off not working

I have a Razer Kraken Ultimate and when was trying to upgrade razer 7.1 surround sound to THX, it gave me the 50% off THX promo code and it worked in the cart but I noticed that It wouldn't let me fill out the billing address, that's when I realized in the URL of the website was "Sg-en" which meant I was on the Singapore website and I live in Australia so I went on to the Australian store and went to buy the THX software from there but the promo given doesn't work on the Australian razer website I was thinking this may be some kind of glitch or because I bought it from amazon overseas is there a way I can still get 50% off.