cannot report declined card

Following - I made an error of judgment on some lovely guests. They said to charge the card on file, I was busy and did not charge until an hour after check out. Card declined. I contacted them and they gave some excuse, they tried to to send an alternative card  via Booking.com message but the card details were blocked in the messages. They would not e-mail because of online safety and did  not have paypal. All communication with Booking.com was useless - just not our problem. Yes I am stupid to trust people, I do not usually collect payment until check out, I like be be sure my gusts are happy. Sadly now I do not trust people, all because 1 ruined it for others :-(