Received a warning letter on fake review.

Hi fellow partner, I just received an official warning letter accusing us on give a fake review and yet we did not give any reviews nor helping customer or asking/begging them to give a superb review in our page. I had been asking Booking.com to give us any evidence of proving if they really think we had given a fake review but they unwilling to share any of it and suggest us to do our own investigation. we had been in the middle of chaos with the current COViD situation and keep improving our quality of service. I wish to know how they define fake review? is there any forum or articles I can have it? I don't want this to happen again, therefore, I ask Booking.com to let us know where we had violated the contract and they lead us here.