I deleted my Gmail account but I keep recieving the notification "Account Action Required" but I can't access the account since it's already deleted. By the way I used my phone to delete the account. How can I remove the notification? I tried everything.
Even if you deleted the account on Google, your phone is still trying to log into that account, and giving you the notification to tell you it's not working. You need to remove the account from your phone too. From the Settings app, scroll down to the Personal section and choose Accounts. Then choose Google from the list, and from the three-dots overflow menu, choose Remove account. Some manufacturers move around the settings on their phones, so while the instructions above are fine for stock Android, they might not be quite right for your phone model.
Note that apps you purchase on Google Play are tied to your Google account, so it's not usually a good idea to delete the Google account that's the main account on your phone. You'd want to follow these instructions if you've added a second account, such as a work email, and it's been deleted or disabled.