Using my Xfinity App I can see that there are devices on my Wifi that do not belong to me. I didn't give out the password to anyone, and it says it is secure. But I can see that the devices are using the internet. I can't forget the devices because they are still connected. Is there a way to kick the devices off so I can forget them or make a new password?
See if they appear here:
I assume you mean the xFi app. Have you checked the online web site for these devices?