Not sure if there's a difference between .BE and .NL (since EU etc) but they've probably got some kind of loophole.
Like "Sure, you can get your own grid feed at non-ripoff prices. But you have to pass through our property and we charge €5K per meter to dig in your cable" - or something like that.
Or "OK, maybe it's not 100% legal what we do. You're free to leave if you don't like it. Otherwise pay up and stfu."
Still, sucks.