Cancellation not possible for late reservation

Hi,

Because I had a very late reservation, I had an overbooking. Contacted the guest that he was just a few minutes too late and that a cancellation was the only option.

But, I was unable to cancel and the guest not cooperative.

Contacted booking by phone, no answer and by mail, the same.

Finally I had a no checkup (which was the intention) but I received the amount.

Question is how the customer will get his money back?