Thanks all for your responses. I agree it's time to move on, my advice to you / the lesson to be learned from this is:
1/ Take a screenshot on the 31st of december of the total of the nights/stays on your account (b/c the information SPG has is not the same from what you see). Once the year is over, the system doesn't carry on all the special promotions.
2/ Deal with it right away and preferably by e-mail. (I agree it was my fault I didn't deal with it right away).