How can I remove a device

I have found a number of lists.  The first under "Home Tab" lists 10 devices, of which 4 are mine and 6 are not.  No way to remove them.

Another list only shows active devices, again no way to remove.

Someone else (not ATT)  posted a different method: sign into Gateway etc.  Click on Wi-Fi. This leads to Wi-Fi configuration under LAN tab.

Then click on diagnostics, then click on resets.  Then a list of resets appears one of which is clear device list  and a clear button. Which clears all devices.  Devices will be re-listed as the system rediscovers them.  Some may stay gone, but my interpretation is that the active ones will appear and little will be accomplished. The person messing with my account must have my p/w, and tracks me through Smart Home.  My thought is to get ATT to install a new modem. If they won't or that doesn't solve the problem, I'll just shift to Cox.  I am not computer savvy so I really appreciate you taking for taking your time to help. 

Thanks for trying our suggestion, @Yogabum. 

First we recommend changing your AT&T account password. If they're able to log in to the app, this will prevent them from doing it.

After this, you'll want to change your Wi-Fi password with our Smart Home Manager app and remove and block any unwanted devices from your network. You can find instructions under Smart Home Manager features, or by watching the video at the bottom of the page.

Please let us know if you need additional instructions.

Raiden, AT&T Community Specialist