You need to call Paypal and tell them you did not receive all of the item back and you don't see why the buyer should get anything until all the original contents are received, not just the packaging. If they refuse to do anything ask to speak to a supervisor. If you still get nowhere try again a few hours later, dome staff are more helpful than others.

If you still get nowhere tell them you are prepared to send them a stat dec confirming that the item was not returned. If they still say no then just tell them that if they do not find in your favour you will be contacting the FOS to lodge a complaint.

I would also put Italy on your exclusion list of countries you do not post to, there are a lot of complaints of parcels going missing and being 'lost' by there customs and delivery services.