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 probab

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.)