Today was an eventful day.
I first went to the house to let the guys who built the cellar to come and get their metal posts. This came as a surprise and took a bit of time.
I then met with Electricien Belgium at COB, because they insisted they could not talk to the constructor anymore.
At Electricien Belgium' place, I have found out they understood that I requested smart house stuff (KNX to be precise) and the house protocol did not specify anything. I have then went with them through the whole protocol to tell them that I only need the cabling to be prepared now.
When I left, they showed me a message sent by the building engineer stating that he would not come on 28/05 because he explained the stuff three times and can't talk to Electricien Belgium any more. Great! I rang the translator in Luxembourg and he confirmed that the engineer will come in the next day.