Non sky devices connected to my WiFi and phone line not working

[martas+laptop]

I have had some problems with control and coercion since 2017, my sky broadband as the owner and adult bill payer is being accessed by now two WiFi extenders neither are in my property. I don't think. My phone line is also now not working and it's not allowing me to remotely remove them as they show as hard wired with an Ethernet cable. There is no cables in the back of the router or sky box. 

[Chrisee]

@martas+laptop your post is quite hard to understand but If there are no cables other than the power and the broadband connection cable the only way devices can connect an extender is by using WiFi.. If you simply change the WiFi password any devices which are not yours will be disconnected. See https://www.sky.com/help/articles/find-and-change-your-wireless-password