From outside, the building has at least 15 floors. Looking from the penthouse down to the forecourt, it has at most 6.
When the captain rings the doorbell and nobody answers, he shrugs and goes away. But either he or his staff would have seen at least 2 people going up to the apartment, since that is why they were constantly watching in the lobby.
Anna's accent keeps switching between German (to begin with) to French (right at the end).