I would check if you are actually paying for the electricity in your compartment. I would be surprised if the socket in the basement is connected to the same circuit as the one in your flat. After all, it would be very costly to integrate each cellar compartment into the electricity circuit of the flat belonging to it.

Plug the Devolo directly into the socket and then into the power strip, so it should work if the socket is on the same phase as in the living room.