Appalling service and refusal to pay monies owed

I listed my property with Booking.com in 2019-2020 and despite providing all remittance advice notes and amounts, booking.com have failed to pay the total amount as per the total remittance. They have refused to pay up saying that I need to provide information regarding the booking discrepancy! It's a simple case of doing the maths. I even spent over half an hour on the phone to their representative Gilbert going through all the paperwork, providing each remittance advice number and the amount owing, adding them all up and then providing information regarding the total amount that was paid and got nowhere. They don't seem to care about those who list their properties for which they earn money and being able to speak to anyone who will take ownership is impossible. Completely incompetent. I would not recommend them to anyone under any circumstances.