If I remember right, that's one of the side tasks needed to complete the chapter? If so, you've unluckily ran into a long standing bug with the game.
Most of the people who have posted about it are in year 7 and have got stuck trying to complete one of the assignments, but can't turn it in as the exclamation mark doesn't show up. It happens if your game crashed/disconnected during the end conversation to complete the task, and you reload the autosave made during the conversation.
As far as I know, there is no "fix" for the problem, other than contacting support. However, being in year 8 you are near 100% likely to get banned if support looks at your account. The only other thing that I can recommend is waiting a few patches, as I've seen someone post that the bug fixed itself after they didn't log on for a few months.