Please help- iPhone 12 Pro Max not working overseas however data roaming is on?

Hello!

I am hoping some technical whizz is out there that can help me. I have two phones

1. An Australian phone with SIM
2. An English phone for london with a sim

Last time I went to London my iPhone 12 ( Australian Phone) did not make any calls apart from Wifi calls, I could not call out locally OR Internationally / could not receive calls. My Global roaming was switched ON with my provider ( telstra) and also ON on the iPhone.

I will attach some images in the hopes someone can tell me something doesn't look right.

***Is it something to do with under the sub catergory " DATA PLANS" it states:

Telstra ON > ( This is my Australian Number )

Used as "Mobile data" > No Sim

This is my london number that for some reason shows on this phone ?

Thank you so much in advancee