I apologize for my late response, and thank you for all of your patience while waiting for a reply. I understand how upsetting this may be, and I'm happy to assist you with this. You should be able to edit how you want to receive notifications on each device, and you can change them there. Be default, they will go to all available devices connected to your doorbell.
Do you happen to have more than one Google account linked by chance? That could be the cause of the double notifications. You can try these steps:
Just checking in to make sure that you've seen our responses. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.