We are just players, we don't see your game. To help you, we need more accurate information.
If you are playing on mobile/tablet.
Open the QUESTS page in the bottom menu bar.
Then on the EVENT tab scroll down to CHRISTMAS 2021 event.
Here are the unfinished Quests for the event listed.
If you click on the small pictures, you can read the tasks. And click on the GO button to continue with that quest. (you wrote that the game says you have unfinished quest)
//Just a suggestion, click on Mr. Thanks in the camp, maybe it helps.
If that doesn't help solve the problem, take a screenshot of that, and one in the map manager to see which locations are closed.
If you are not playing in English, set the game to English for that short time so we can understand the text. Thanks.