How would someone use that code to hack into my GV account? Wouldn't they also need to know my password or have access to my e-mail account to login or to reset your password?
Because OP specifically mentioned Google Voice, my guess is that it was a phone number "ownership" code, rather than a 2FA code per se.
The attacker was probably trying to create a new Google Voice account forwarding to OP's phone number. They could then use the new GV account as its own "legitimate" phone number in order to engage in other scams.
(Alternatively, OP's password might have already been compromised, and this was the last stage of a targeted attack by someone trying to get into their account.)
I don’t use GV, but presumably if they can make Google send you an auth SMS then they have already input your password. I’m guessing it was leaked in some big password leak, and not phished at an earlier time.
