How do I become Grand Duke in the Battle Chateau in Pokémon Y?

So I became Duke in the Battle Chateau, battled all trainers, including Gym Leaders and the Elite Four (I know for sure since I kept track of it, taking the list and crossing off every trainer after I defeated one until I had them all), became the Champion, tried leaving and re-entering and I still didn’t become Grand Duke. What should I do?