Kingdom Hearts KhI 3rd District problem

I'm running like a maniac, I've read 100 walkthrougs, but I can't go to third district. I've already talked to Cid, and I've received the book, also I've sealed the keyhole in traverse town, and completed the Phil's coup but I still can't go through that door. The door in the secret waterway isn't working for me too, what am I doing wrong?

 

You know where you first fought the Armour?

in that part of the town theres a key hole that opens the 3 rd district i think​

 

You're referring to the door with the fire symbol on it, right? Just lock on to it, step back a few steps away from it and hit it with fire. Then you should here a little tune and you can go through the door =).

 

at first you can only get to the third district through the second district. after you release the door from there you can go directly from the first district.

If your referring to magician's study (merlin's place) then you need to cast fire on the door and enter that way before you are allowed to enter through the waterway.

 

There's no "door" in the secret waterway.
And i thought you needed to go to that place to seal Traverse Town.
And just go to the place you fought a armor,then when you see a door with a fire symbol use fire on it.