Now, do not go further. After the initial panic and thoughts of having to starting again and even of all the money you have potentially lost, don’t worry there is a fix for those who sign in through their Google account.
Update: Niantic has released an official help post for this for iOS users. Try that before the below.
Some have suggested making sure you pick the exact username as before and you will get the game back. However this did not work for me.
Here is what did work to recover my account:
In your browser sign into Google. Navigate to https://myaccount. google. com/security#connectedapps and remove the permissions for the Pokemon Go app. Delete (the hardest part) and reinstall Pokemon Go. Sign in with the email associated with your Pokemon Go account. You should be in with your account recovered!
Thanks to /u/emil129c on Reddit for this fix.
Did it work for you? Do you have any other suggestions? Let us know in the comments!