Refunds for canceled bookings

Hello, please help us.
We are writing to you regarding a reservation made by a booking user on Oct 31. 

During this period, I tried to contact and verify the guest several times. However, we did not receive an answer from him. Today we contacted him on WhatsApp and he told us that he is unable to visit, but he does not cancel the reservation and refuses to pay the money. What can we do in this case? We have refused many guests during this period

IATA/TIDS code: PC029090