If you booked with Booking, and the hotel called you back, and told you they don't use Booking any more, how do you imagine did they get the information needed to call you back and knew of the booking?

What you have here is commission fraud on behalf of the hotel against Booking.com, and if you call back Booking.com and tell them about it, they will set the hotel straight.

Or you get back to the hotel, tell them you understand how commission fraud works and if they are willing to split that commission (18%) half and half with you.