How to remove your Fonts.com account
From their help forum:
You can downgrade to a free account from the ‘Plans and Pricing’ page, which will cancel your billing.
To truly delete your account, send your request to: email@example.com.
Helpful Trick: Removing online data
Helpful Trick: Remove third-party logins
If you signed up for Fonts.com using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Fonts.com. Click here to find out how.