Non-payment

Sorry in advance for the lengthy explanation. 

To being, we received a booking from booking.com for a two night overstay in August. When the guest arrived they explained they had booked via last minute.com - we were unaware Booking.com could even advertise us via a third party as we definitely do not advertise on booking.com. The guest informed us he had pay via a last minute.com voucher. I went on to booking.com to retrieve the card details and they were indeed a card from last minute.com. I was unable to take payment as the cvc number was missing. The link has since expired. We are now nearly 3 months since the booking and still not been paid. I have spoken with numerous people at Booking.com who ensure they will get in touch with last minute.com and ask for new card details etc but I never heard anything back?  

Any advice would be greatly received. 

Thank you