I use my password manager to find unused accounts and delete them
This is a really bad title, but summarizes what I regularly do and recommend doing regularly. A nice side effect of using a password manager is, that it gives you a perfect overview about all your accounts. From time to time I go through this list (at the moment I have saved over 200 logins) and see if there are any services I no longer use and need. If this is the case I go to the website, log in and try to find the settings to delete that account.