LAN extremely slow?

I got a lan cable because my wlan is only 5mbs download on my xbox despite 50mbs line but with lan cable is much slower than with wlan please in quick help

What does your network topology look like?

Is the XBox really connected directly to the router?

Switch off all other devices that use the Internet and disconnect all LAN cables from the router, except for the cable of the XBox and restart the router and the XBox. Is it still slow then? And what happens if you connect a PC / laptop with the LAN cable instead of the XBox? How fast is that then?