If your WiFi has been hacked you need to change the security password on that WiFi router from that routers admin page (for many WiFi routers it’s https://192.168.0.1.or 192.168.1.1). If they’ve reset the routers password, disconnect it from your internet world connection, reset it with the hardware button, and then set it up by plugging it into your computer. Set it up over that ethernet connection before you reconnect it to your internet connection (and set a good strong password - one for the router admin account, and one for the WiFi connection password).