Oh, @Giulia1049 , you have reached a forum of hosts who are discouraged and exhausted by a system that expects them to act as their guests' travel insurance without the benefit of having received premiums.
But here you go: Give Airbnb a call and explain your circumstances. It's all you can do, and you will likely get your refund.
Writing here does nothing except make the rest of us feel sorry for a fellow host who is about to lose income she cannot recover, as you blocked her calendar and the dates have passed.
I hope your travel companions have recovered.