Sorry to hear about that. Have you migrated your Nest Account? How are you trying to remove you 1st Gen Nest Aware?
You can check this article on how to Troubleshoot 2-step verification if you can't receive emails from Nest. You can try these steps if you want to cancel your 1st Gen Nest Aware subscriptions:
1. Visit https://bit.ly/3rEq0Tu.
2. If not signed in already, select Sign in with Nest.
3. Select Cancel subscriptions.