I explained in my original post: when I booked the tickets I have been given the option to select seats and I did that. At that time (in October 2014) the seats I selected were not showing as premium seats so I selected them (the same seats in 44K and L in my first and forth leg of my itinerary i.e. AF 351 and AF 356). The itinerary is starting on April 18 2015 (first flight). Now, yesterday, tweeting to AF and having someone look at my reservation for some different question I had (i.e. connection in CDH Terminal 2) they said they noticed I have two "duo seat" seats and I have to pay for them. My questions are:
1. Why do I have to pay for them if at the time of booking they were not premium seats?
2. If I don't pay now, what will happen at check in time? Unfortunately now there are no 2 regular seats together showing available.

Thank you for the link. I saw that but like I said I am not just collecting information I am looking for some advice.

More then that, yesterday a genius from Expedia (the site I booked from and witch I called yesterday to complain or resolve the problem) moved me from my "duo seat" seats on AF356 to some regular seats in the middle of the aircraft and couldn't put me back to the original seats (because they are now premium). A lot of incompetence and a lot of greed from AF I guess.
I am just wondering if anybody else experienced a similar scenario and what they've done. Thanks