disconnectedinaustralia Welcome to the community!
There are several possibilities, which you can test as a solution:
1. solution
Log in to MyUPC and set the roaming limit higher. You can do this via another cell phone that still has internet access or via hotspot WIFI of a café. This has the consequence that your cell phone bill can be high when you are back.
2nd solution
Activate WIFI Calling on your device and connect to an existing WIFI. You can then make calls via WIFI.
Greetings
Daniele