an old Italian (?) horror about a boy that was cut into pieces

[vulpix]

The movie is in color, released supposedly in 70s-80s.
So, there was a boy named Giovanni who went to an organised tour to some factory with other children from his class. Don't remember why but he was cut into pieces during it.
After some time his parents heard a knock on the door. They asked: "Who is there?". And the voice behind the door says: "It's me, Giovanni!"
They open the door and see a dismembered body of their son on the floor.
These are all the details I could recall about this mess. Please help!

[retrorussell]

Possibly DON'T TORTURE A DUCKLING?

[vulpix]

Possibly DON'T TORTURE A DUCKLING?

Thank you for an answer! But unfortunately it was a different movie, I've just checked yours it has no such scenes :(