Booking.com Is a Terrible Website, Can't Be Relied On, Reservation Declined

I booked a place in Kavala, Greece through booking.com. By the time I made the booking I was on vacation in Albania. In fact, the apartment that I booked had actually been booked by another family through airbnb and because booking.com didnot refresh the website in timely manner, I booked a place that was already booked by someone else. I did not have proper internet connection.. I was about to start my journey and by chance I realized that my reservation has been cancelled because of booking.com's mistake. I can not accept this mistake.