I did everything the quest needed, but it's still not completed.
Please read the quest description carefully. Many quests have to be solved in a very specific wa. Some examples:
- Get a province with your army. This means that if you get it by negotiation, it will not count! If there is a "?"-icon, you can move your mouse over it to potentially get a hint.
- Get a sector in an another province in the north of the province. Check if you really looked at the north province. Similar missions are usually directed to provinces that are not yet discovered, so let your scout go there first.