If you have Silver, Gold or Platinum package, please go to your support center to recover your service account [Menu>Support].
You can also go to this article [1], and click on “contact the Compute Engine team” to recover your service account. Please include your project ID and default service account you want to recover in the case.
[1]https://cloud.google.com/compute/docs/access/service-accounts#newserviceaccounts