I am so sorry to hear about this awful guests @Riccardo298
If this is the second time it has happened, I wondering what measurements you can put in place to vet your guests more effectively? Do you have CCTV and check it on arrival/check out? Do you only accept guests with photo ID? Do you ask guests about the purpose of their trip.
However I think it is pretty poor of you to make comments like "They put some third country national on the phone to apologize repeatedly and keep me waiting for an hour just to say they could t get ahold of anyone in the right department".
A. You can message Airbnb to report the damage you don't need to wait on the phone
B. You can look on Airbnb Help for instructions on how to put in a claim
And you should never keep valuable family heirlooms in an Airbnb. Much too risky. If it is irreplaceable it shouldn't be left in a commercial rental.