Hello @Liliana74
I am sorry to hear this. Your host can cancel the booking at any time, so I am not sure why they are saying they can't cancel. Unless there is an emergency, it is bad of them to leave this so late to tell you.
Make sure you keep any conversations on Airbnb messaging so there is a record.
I would call Airbnb now and let them know the host has told you they are cancelling but can't cancel the booking. Airbnb will contact the host and get the booking cancelled. They should also give you a discount voucher toward a new booking and return your booking. You can also ask them to help you find somewhere new.
You can find contact details for Airbnb at the top of this forum in the Contact Airbnb post.
Good luck