I have used the Pokemon bank tons, and I've already picked up my free BP, but I was never told about Celebi when I used Pokebank, and I certainty have never received it. The only thing I can think of is that I'm using the 30 days demo version. Do you only get Celebi with the purchased version, if not is this just an error, and if so is there someone I can report it to and finally get my Celebi?
No you can get the Pokémon Bank Celebi on your Free Trail.
For help getting the Pokémon Bank Celebi watch this walkthrough video here.
Hope I helped :)