Method for filling and closing a package including the operations of introducing two arms through the mouth, each one having or bearing a gripping tool and impressing a mutual distancing movement on the arms to expand the package with a retention mechanism which operates outside the package to grasp the walls of the package arranged between the arms and the retention mechanism while the retention mechanism approaches and fits over the gripping tool of each arm, such that when the arms move in the direction of the mouth of the package, the arms carry the grasped walls of the package to produce folds towards the interior of the package. For flexible tubular net packages, the at least one gripping tool on each arm has the shape of a protuberance and that the method includes passing through a wall of the package with the gripping tool