Good day, several years ago, I have a very similar problem with CommBank and accessing online banking from outside of Australia. The branch and my Relationship Manager wanted me to use the NetBank App but at that time the SMS message for two factor authentication (2FA) for some reason would only work within Australia (not to an overseas phone number).
We solved the problem by using the CommBank dongle technology and that does work here in Thailand, Philippines, and Canada. Most of the time when I login from overseas, I have to give it a second shot at logging in, and it always works on that second time.
As the CommBank is trying to phase out the dongle technology, the bad news is that you may have to be physically present in Australia for the CommBank to provide you with a dongle - in my case it took about 10 days for the dongle to come through to a branch in Brisbane and to then to activate it.
Good luck in getting a dongle without being physically present at a branch in Australia. Cheers and best wishes.