I would instead look at your routers home page(settings). These setting can usually be accessed by typing in the up address of the default gateway on your browser. You can find the address of the default gateway by typing
in command prompt.
Most routers here usually have an option too see currently connected devices. Go there. Usually in the list it will give you a list of devices with their local ip addresses, MAC addresses, and most of the time the name of the device.
Do the above when you think the person who has your WiFi password is using your WiFi, then look at the list and see if you see a suspicious device. Block the suspicious device if there is an option too.[/code]