I have an ISRA connection point in my apartment but it's not connected to the switchboard

Hi! I want to subscribe to KPN for my apartment. The website says my apartment is connected to the KPN grid. I have what I think is an ISRA 2 socket in my place (the cap is missing) but the other end of the cable doesn’t seem to be connected to the switchboard of the house.

It’s a house separated into 3 units: a shop on ground level, apartment A on the 1st floor and apartment B on the 2nd floor. I’m unit A and was told this apartment didn’t “have internet” when I moved in and that I had to share the connection with my neighbor, in unit B. But his wifi is often down (it’s KPN too so I hope it’s not a problem with KPN) so I want my own connection.

I’m not sure how all this works. I have the connection socket but I don’t know why it’s been disconnected from the switchboard. If I become a client, can a technician connect this? Does it cost money?

Attached, photos of what I think is an ISRA 2 (sorry, I’m new to the Dutch Internet) and the switchboard with the the end of the cable not connected. The 2 other cables could be my upstairs neighbor and the shop.
The shop is also connected to another Internet provider (the Z one).