A device I have no knowledge of, has logged into my WiFi. What are the steps block them and to prevent this in the future
They can only log in if they know your SSID password. What is the description of the device?
I can certainly check this for you from here if you would like. To protect the privacy of your account, can you provide your full name exactly as it's listed on the billing statement? To send a private message click on my name, then click "Send a message".