Recurring charges -- especially things like insurance -- are special. They are often submitted without expiration dates. Other processes exist for larger recurring billing customers to have card numbers and expiration dates updated by the customers bank in case of change. Sometimes its your bank that allows charges to go through on an expired card if they determine it to be a recurring service charge. This is why it's often not sufficient to request a new card number if you are trying to stop a company from continuing to charge you for a recurring service. While a few small companies may guess at the new expiration date, in normal cases they don't need to because its not needed.
Most credit card agreements also detail how automatic payments can only be stopped by contacting the biller and, until you do so, the charges can post to your account even if the account is closed.