I canceled a premium Yahoo mail account five years ago and so did my partner.
We both just found a $19.99 bill on our credit card bills for the non-existent Yahoo mail accounts. Fraud, incompetence or some combination.
Check your credit card account if you have ever given Yahoo a credit card number. Don't waste your time phoning Yahoo, they will do nothing. Call your credit card company and have the charge removed.
Update: After five phone calls, I finally got a supervisor who found the account I am being billed for. Indeed, a Yahoo email account had been opened for a friend in 2002 and never used. Never used. I've paid $100 for that account by now.
In banking the law requires that all account holders with accounts with no activity for three years be notified. Bank of America lost a sizable class action lawsuit in the early 1970s when the Bank claimed that they couldn't find 100,000 customers. When details of the 100,000 list was published it include Herb Caen and Joe D'Maggio among many notables.