I'm sorry to hear that you're having an issue accessing your thermostat. I'd love to help.
Here's an article with some troubleshooting steps if you couldn't sign in on the Nest App. If you're able to login but couldn't find your thermostat, make sure you're signed in with the correct email address. If so, try checking for other available structures where your thermostat might be connected. Check out this guide on how to switch home structures.
Please let me know if that helps.
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