Thank you very much for the answers!
We agreed on exposed concrete because we only want to paint the ceilings, which is why hanging them up annoys me so much. And, as you already mentioned, I also don't see the point of completely hanging them. Later we have an appointment with the site manager. Also to find out what the original plan was. We have two site managers, and one of them already started stammering a bit when I hinted to him that this can't work, so the boss is coming today. We chose a construction company from a nearby village, so not my big company, I hope they are accommodating since they rely much more on a good reputation. But why is 2.40m too little? I have lived my whole life in rooms no higher than that and have always been satisfied?