Can I ban a device connecting to my wifi

[Lishasiddiki]

Can I ban a device from connecting to my WiFi? Basically, I notice this device always connected to my WiFi. I have no idea who's it is (might be one of the kids, they're denying it is) if I have the MAC or IP details of the phone ( I can get from virgin connect) than can virgin ban it? 

[Client62]

Do not block and unknown device, it might turn out to be your heating system / home alarm / or an office VPN !
It can only be a device that has either been plugged or has been given the SSID / Password.