Am i being scammed?

Hi Travel folks. We have booked a stay for 3 nights in an apartment through Booking.com. The listing was a family suite containing 1 bedroom with a double bed & a single bed. Bedroom 2 with a double bed. Cost advertised on Booking.com was €300. Upon arrival only 1 bedroom was available to us (a family of 4). We told the owner that we had booked both rooms. He said that we hadn’t paid enough & that it would be another €100 for the second bedroom for the 3 nights.

We argued that we had paid for 2 rooms on Booking.com. He showed us his booking which looked like it may have been a different system (or maybe the Booking.com back end - i dont know) which showed that we had only paid enough for 1 room with the 2 beds. He made the extra room available to us but said we would need to pay him cash for the use of the second room.

We kept on pressing that we had paid as per our booking confirmation but he was adamant that we owed him the money & that booking.com was wrong. He is expecting us to leave the cash in the apartment. I have tried to contact booking.com but can only get their AI chatbot which keeps on trying to get us to resolve it but talking to the owner.

Is this a known scam? Should I just not leave the cash? I would rather pay the extra to booking.com but cant get through to them directly.

Any advice would be greatly appreciated.