This seems to be happening a lot. Your the third person I have heard this happen to.
I implore anyone using coinbase to use Google Authenticator 2FA. I also don't think it is a good idea to link your google account to your phone number. I don't know how these people are finding people to hack but this is unnerving. I only used coinbase to buy BTC and ever since it has gone up I haven't used it at all. I'm sorry this has happened to you man