Reactivate your canceled Google Fi service
If you recently canceled your Google Fi service, and haven't transferred your number to another carrier, you can undo your cancellation from the Google Fi app or website for up to 7 days. Otherwise, you can contact Google Fi Support to re-activate your account for up to 60 days after cancellation.
If your Fi account was canceled more than 60 days ago, you can open a new Fi account directly from the Google Fi website.
If your Fi account was closed, you can contact Google Fi Support to pay your outstanding balance and open a new Fi account.