It still unclear whether the mentioned(problematic) user account is receiving notifications/updates regarding Google Cloud Platform and/or it connected resources.
By default, a user account with '
owner role' or '
billing account administrator' role in a specific Google Cloud Platform project will receive notifications/updates regarding the the GCP project. You can find more details about the categories of notifications and its default contact in
this help center article. If the project is a part of Organization, you also need to check whether the user account is still have the
mentioned roles at the Organization level.
By looking at your statement, it seems like the notifications are coming from Google Cloud Platform. So the particular user account may be still having the owner role(or billing account administrator) in that GCP project. You might need to follow either of the below mentioned steps to manage the notifications connected with GCP.
1.
Revoke the necessary role for the particular user account.
If the above mentioned steps didn't help you with your situation, then you need to seek
additional assistance from Google Cloud Platform as a next best step.