Be careful when paying through them

When I made a booing with Booking.com I paid the full amount as required. However, they did not pay that full amount to the hotel/lodge. I then had to pay the difference to the hotel/lodge when I got there. Booking.com has not refunded the difference despite being requested to do so and whenever I phone their customer service line on answering they drop the call numerous times. I have also messaged them on their app and via email and have not received any response since. This has been ongoing for a month and a half.