A refill device for a container having an opening to a cavity including a first connection element with first connection means for removably connecting the refill device to the opening, a bag first part filled with a substance for housing in the container, a neck and a connection part between the neck and the first part, and a flange, a pump, a ring nut element connected to the first connection element to connect the pump and bag thereto, the first connection element including a body with an upper part including an upper opening delimited by a wall for resting a portion of the flange and connection means, a lower part including an opening and first means for removably connecting the refill device, the first connection element including second connection means for removably connecting a protection element to the first connection element before associating the refill device with the container.