Yay! As I suspected, the cabling from our apartment to the backbone in the cellar wasn’t installed. Apparently there are only 24 ports, but 30 apartments…
Anyway, we now have net connectivity. Don’t know how long it’ll last, I tried to set us up with the ISP but they couldn’t determine where I was connecting from. So I’ve taken it up with their support, via email…
Next step: internet telephony.