Well i bounced the question of prof / professeur off my neighbour's kids who are at secondary / high school, and to a person they replied prof or professeur. They regard "instituteur / institutrice" as a primary school teacher, and " l'enseignant(e)" as a general word for those in the teaching profession, although if it's at university level "professeur" is the norm. They should know and i'm not going to argue with them. And anyway, the prompts were clear and specific just as Cécile said so i can't see what the issue is ??