Is it permissible for me to dispose of a commodity that reached me by mistake, after I have exhausted all means to reach its owner without success, and I have learned that returning it is impossible, and I have paid its shipping and customs fees?

If you receive a message addressed to your name and address, and there is nothing to indicate that it was sent in error, then if there is a possibility that the sender intended to send it to you (as a debt or a gift), there is no harm in benefiting from it after investigation and failing to find the sender, while guaranteeing it to its owner should the opposite become clear. However, if the possibility of the shipment being for you is remote, then piety dictates preserving it and treating it like lost property, such that it is kept or sold and its price is kept for its expected owner, or it is spent on the public treasury if his appearance is not expected, and this is done by those in authority if there is no ruler or if he is unjust.