Booking.com Trouble To Change Reservation Dates, Bad Attitude To Earn Money...

I made a reservation ın Ca' Princess Hotel in Venice throughout booking.com. The option I choose was non-refundable if reservation is cancelled. Anyway, after i confirmed the reservation I realized i made mistake on reservation dates. I contacted directly customer center, I explained the situation and requested date change. They told me they will call and forward my request. But Ca' Princess not replied. Costomer service agency told they will send email expailnin the situation and asking for my request. Today I got a reply email from booking.com that my request was refused. I directly contacted with customer service and re-explained my request that i dont want cancellation, just date change. Reply was it is not under their control, only Ca' Princess can decided waht to do and how to do. What does it mean? I paid almost 400 Euro and due to 1 small mistake, I lost it for unused reservation. Either booking.com or Ca' Princess didnt care my request, and just focussed on free money they earn by doing nothing and from unused reservation. This is either fair or ethic. How can someone accept earning this kind of money which they get by doing nothing. I tried to reach Ca' Princess by phone, after several attempt some one replied to my phone. I re-explained situation and repeat my request. During conversation i lost the connection somehow either by signal or Ca' Princess closed the phone. Then i tried to reach again several times, no body replied. I tried to reach through whatsaspp, same no one replies. I just requested little/small help. But attiude from both side (booking.com and Ca' Princess) was not friendly and hospitable. I suggest all people who will read my complaint, not to use this terrible not customer friendly travel web site booking.com or Ca, Princess Venice Hotel. I hope you will loose more than what you got from me by doing nothing...