I presume you are still using it in the Australian store since you are only on holiday in Thailand? It should continue to work. Conceivably a service provider could detect from your IP address in which country you are located and prevent service if that was in violation of terms of service. I have never heard of anybody preventing that in terms of doing it at the payment method level though.
Apple Media Services Terms and Conditions - Legal - Apple Media Services - Apple
- A. ”Our Services are available for your use in your country of residence (“Home Country”).
And: "Certain Services and Content available to you in your Home Country may not be available to you when traveling outside of your Home Country."
Again, I am assuming you have NOT changed to the Thai store. If you have then that makes a big difference (and you should have told us that at the start).
Contact Apple Australia. You will have to do so by chat since I don't think you can call them from another country, nor have them call you. Choose your country or region - Official Apple Support
Select your country (if you do not see your country, also look for "other" regions; e.g., "Other Africa"), then "Choose a product". Click the "show" item under each category for more selections.