Someone else on my network

[#1]

Does anyone know how i can see who is logged on to my router/wifi connection/network?  I cannot see a link when I log onto my Plusnet account.  Many thanks.

[#2]

If you log into your router you are usually able to see all network connections there.

[#3]

Whereas Plusnet neither know nor care.

[#4]

why would plusnet know?
only the person with the router can give access to other people? by either telling them the wifi password or letting them connect an Ethernet cable to the router.

and why would they care?
it's the responsibility of the account holder to ensure their network is secure.

and to the OP, all routers show you connected devices.
and the easy way to stop any unauthorised connections is to simply change the WIFI password, and unplug any unauthorised ethernet cables.