I have had the same problem with KLM and AF.

On Saturday I fly out of JNB to Paris and currently my seat is 82G. I am on a M fare and 006 ticket stock. I was able to call Delta and they got me the seat in Premium Economy. (I managed to get the seat in 1 Call) On Delta's website it shows "Seat Requested" on the AF and KLM site it shows that I am in 82G. I am crossing my fingers that at T-30 my seat does not get reassigned back to a middle seat in economy. I have signed up for an account on KLM using my Skymiles number. I do not have a flying blue number.

In December I flew on KLM out of AMS to JNB and was able to get an EC seat as well. That one took 5 or 6 phone calls to finally get it to stick. In the end it was Delta that got the seat assigned. I tried calling KLM in Amsterdam and they said I would have to wait until t-30 to get an assigned seat. Also tried twitter and they said the same thing.

Also, it will be helpful to get the Booking Code for AF. Then you can go to the AF website (or KLM) and see that your seat is assigned.

Don't give up. Hang up and call again and get someone else. It can be done.

Good Luck.