Logging out of accounts

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Thanks for taking the time to reach out to us regarding keeping your account and services secure. Did you mean you want to log all devices out that may be logged into your account? IF so you can try these steps, 

https://www.xfinity.com/support/articles/manage-wifi-devices-my-account
How to Manage and Remove Registered Xfinity WiFi Devices

To remove or rename a device registered to access Xfinity WiFi hotspots:
    Sign in to My Account or the My Account app and click or tap the Services tab/icon.
    From the Services page, under Internet, click Manage Internet.
    Scroll down to Xfinity WiFi Hotspot Connected Devices and click Manage Devices.
    Click Rename to edit your device name.
    Click Remove to remove your device from the list of registered devices. A confirmation message will appear.
    Note: If you've reached your limit of 10 registered devices, you must remove a device before you can add another.