@Chardly The game triggers Charlie's response after visiting the last room of the sewers (a safe area). Once you reach there, a new task will appear to open up, which will tell you to find a ship by the docks. After that, you should be able to talk to Charlie and end the original task. It's just the game mechanics screwing up a bit. Backtrack into the sewers, and you should be able to progress.
 "The Last Stand: Union City"){kind=icon}