Finally heard back from Melia customer services
Apparently they no longer email you about the birthday surprise, no write to you, nor send you any sort of message. They still do it, but you have to be psychic or something...
Around the time of your birthday, you now need to log into your account, and go to
My Promotions (new option between My Booking and My Points). This year's offers are an upgrade or 20% off:
