Confirmation letter sent to place with no postal mail

Hi !

I own a country house that is located at a place where postal email will not be delivered. I have been running this business for many years by using my own site (https://lagalea.net), our Facebook page (https://facebook.com/lagalea) and Airbnb (https://es.airbnb.com/rooms/285941) 

In order to register this property in Booking.com a letter was sent to that address, but it will never be received.

I asked Booking support to send that letter to my home address, but I never received an answer.

The question is: how can I get the confirmation code for this property ?

Thanks in advance,

   Antonio