Booking.com Car Rental Complaint. Charged in Full Despite Quick Cancellation

I rented a car for one day to use on Samos Island, but due to incorrect dates, I canceled the reservation less than an hour after receiving the confirmation email. Despite canceling within this short timeframe, they charged me the full amount, citing their cancellation policy of canceling 48 hours in advance. How can I cancel 48 hours in advance for a reservation made just one day prior? This cancellation policy is unreasonable. Customer service only responds by pasting the cancellation terms and is not helpful at all. Unlike other car rental companies that charge a small fee, Booking.com takes the full amount and offers no assistance. I will never use Booking.com again.