Hi Cupart,
Welcome to the daily world of AF. Please dont take it badly, but it is a bit fun to see someone who has made such enthusiastic posts in this forum discover why many of us are bored with AF & FB. I have no experience with KL so I wont mention them. Good to see pax who are increasing their FB level rather than reducing it as most of us. But maybe you will revise your opinion when you start to fly more frequently.

Let me ask two questions: 1) is it an award and 2) is it KE metal?
If it is a paid ticket you should simply call the AF call center (use the Elite hotline) and let them solve it. No reason to call FB. Actually, even on a FB booking you can call the Elite hotline for seat assignments.
If it is KE metal, it could be that AF is allocated some specific rows and that you dont have acces to the better rows.
Again you have plenty of time to get better seats.