Possibly because they have not paid them.
In Spain (I believe that) a debt, for which payment is not demanded within 4 clear years, is unenforceable. However, once demanded they have another 4 years to enforce the payment.
That applies even if the person from whom the debt has been demanded may not know of the notification, i.e. maybe they have moved and not notified the claimant of their new address.
This message was last edited by johnzx on 21/11/2015.