In the end, I had to put my simcard into a new phone and verify.
Sorry I can't be of more help right now with the access issue.
But, some advice from my lesson: EVACUATE FROM GMAIL IF YOU HAVE ANYTHING IMPORTANT IN YOUR EMAILS.
Switch to an email account using a domain you own (and ideally use a paid email provider so you can at least contribute to them sticking around).
I only have about $20k worth of dev work locked up in it, but it's gone.
Fuck dropbox.
iirc google requires another email as backup address for exactly this kind of situation. don't you have one set up instead of just a phone number?