Why an agreement beats a setting
An older person is not called in order to break into their phone. They are called so that they withdraw the money themselves and hand it to a courier. No setting stops that.
What stops it is a rule agreed beforehand: in this family money is handed to nobody and transferred nowhere until a specific person has been reached on a specific number.
The conversation with a teenager runs differently
A teenager is deceived through advantage and through trust in a familiar account rather than through fear. A request for money arrives from a friend whose account was taken, and it looks entirely ordinary.
The agreement has the same shape and different content: any request for money in a chat is confirmed by voice, even when it comes from a best friend.