How do I get info on guests?

Good day

The situation that we are currently facing is as follows:

We bought a guesthouse which was on booking.com.

Unfortunately we have to cancel 2 bookings, but the previous owner already cancelled her account with booking.com - thus we do not have the contact information of these guests.

I phoned a booking.com number and was told that she need to confirm the details and then will call me back.

Any advice will be helpful,please.