cog_unload, not __unload, whoops.

announcedaily/__init__.py

@@ -6,4 +6,4 @@ from .announcedaily import AnnounceDaily
 def setup(bot: Red):
     daily = AnnounceDaily(bot)
     bot.add_cog(daily)
-    bot.loop.create_task(daily.check_day())
+    daily.announce_task = bot.loop.create_task(daily.check_day())

announcedaily/announcedaily.py

@@ -1,6 +1,8 @@
 import asyncio
 import random
+from asyncio import Task
 from datetime import datetime, timedelta
+from typing import Optional
 
 import discord
 from redbot.core import Config, checks, commands
@@ -38,10 +40,16 @@ class AnnounceDaily(Cog):
         self.config.register_global(**default_global)
         self.config.register_guild(**default_guild)
 
+        self.announce_task = None
+
     async def red_delete_data_for_user(self, **kwargs):
         """Nothing to delete"""
         return
 
+    def cog_unload(self):
+        if self.announce_task is not None:
+            self.announce_task.cancel()
+
     async def _get_msgs(self):
         return DEFAULT_MESSAGES + await self.config.messages()