I did nearly continue the deliberate poor grammar by arguing that of course I wasn't 'defrauded' - that would mean that someone had removed the fraud!The crime is called fraud, so it made sense when the OP said they got frauded. Didn't realise it's actually defrauded!

Regarding the 'how it happened' - the fraud people seemed singularly uninterested in the question as far as I could tell. Maybe it costs them more to spend the time trying to investigate than its worth to them?
Not so much intercepted, but it's possible someone can clone your SIM, and they don't need access to your phone to do it.
I only use mobile 2fa for stuff I don't care about.
Password managers and my main Google/Microsoft accounts are secured with a pair of Yubico FIDO keys, and printed and stashed recovery codes. Definitely do not use SMS/phone for securing password managers and the like.