HN user
Of course you can keep your provider. It's called roaming, per OP story: "I am travelling to the UK and did not want to have *roaming* on my Australian phone."
For cheaper rates than roaming, typically you install a secondary eSIM for the country you're traveling. 99% modern phones support dual SIM for this reason
The problem is the rapid succession of changes to recovery phone number, country, cellular provider. There is no way to differentiate, at scale, between an account takeover currently in progress that needs to be stopped immediately to minimize damage, and a legit user deciding to change all his personal info at once.
30 day cool down period is a reasonable response, at scale.
OP triggered every possible red flags for suspicious account takeover in Google systems: deleting his recovery phone number, moving to another country and cellular provider. And then he gets surprised that the account is in 30 day cool down period??? I don't understand people sometimes.