By leaving the Hall of Echoes, do you mean that you reloaded an earlier save? You can use the dragon stone in the dragon sections to get back to the battle tower, but the teleporter should be disabled to prevent you from going anywhere but back to the Hall of Echoes.
Are you sure the Note from Maxos isn't in the quest item section of your inventory? Reading it at the entrance to the Hall of Echoes should remove the ice (or whatever) blocking the way in.
