Booking not yet Confirmed Cash Withdrawn

I sent a request through to the host asking him for the exact location of his home and was prompted on the system that he would need to reply within 24 hours. He did with the address and before I could confirm, the booking went through and the amount was taken from my account. There was no payment screen – I did not authorize any payment. How is this even possible? Surely I have to go through a process of entering my bank details and authorising payment?

I then proceeded to cancel the booking and was told that I would only get a 50% refund in ten days. The host said he only received payment the day after I arrived from. Where has the money gone in the mean time? I then proceeded to request the balance from the host and have had no reply, which makes no sense as he was quite prompt in replying to all my messages.

I have reported fraud to my bank on this transaction but the point is how was it even possible for Airbnb to have this authority over my banking details? Is this what a host can do, confirm a booking and payment from his side without the consent or authorisation from the prospective guest? Because he has a strict cancelation policy, he can now keep 50% of my money, from a booking that was never authorized by me? I am extremely disappointed in this system.