SIM swaps are relatively easy in Australia, requiring only some fairly simple social engineering of staff in a phone store.
Number porting is trickier, requires a name and account number (or DOB in the case of a prepaid account) of the victim and they receive an SMS informing them their number was ported in advance.
Yeah getting thee account ID can be a pain, I've learned that the number in the UI and bill is not the identifier they want. Security by poor implementation.
I couldn't even get my own number ported in Australia (to a new provider on a new SIM). The old provider said the authentication failed. I gave up pretty quickly and just went with a new number.
That requirement is there for new or ported-in services.
But when you Sim swap, it's tied to the same account. So if you can convince the minimum wage hourly wage contract employee at a franchisee that you're the account holder, no worries.
Worse, most of those stores are using generic accounts and/or passwords.
Telstra years ago had a policy along the lines that store accounts could be not tied to a specific employee, so long as the store manager/team leader rotated the passwords and kept records. in reality it's something stupidly guessable that rotates only when required and all the staff know them.
Optus effectively has the same thing - I had an issue getting a SIM established and sat with an employee for about an hour as they re-rolled the account about 10 times. By the end I knew the passwords for all the accounts in the store, plus other identifiers and numbers.
Number porting is trickier, requires a name and account number (or DOB in the case of a prepaid account) of the victim and they receive an SMS informing them their number was ported in advance.