This just happened to me. The same timeframe, the same vector of attack, but a different target. They wanted my Twitter handle. Fortunately it was an old handle that Twitter had locked down and was not transferable. The hacker succeeded in making me lose my handle for a few days, but some friends came to my aid and I was able to get resolution through Twitter support.

My telecom company was helpful at first, but then we began to see circle-the-wagons behavior from them. We were at least able to get the call forwarding off of the account, but they would not tell us any details about what had happened on the account.

Until your story (and even now) I'm not exactly sure if my hacker had been able to forward the text messages or simply routed the phone call to his phone and using Google's password reset process was able to get a robo call to accomplish the same thing.

All of this is seriously making me consider creating my own 2FA service, only slightly better.

One quick recommendation I would add would be to put a passcode on your account with your mobile provider. Just call them and say "I'd like to add a passcode to my account", so you can at least add one extra layer of security there.