Booking.com making unauthorised deductions and then dragging feet on refunding the money

I made a booking for December at Casa Marianna, choosing a "pay later" option. Then booking.com starts deducting payments. Apparently the room I booked, even if you cancel 11 months in advance, you are still liable for the full amount. This is NOT acceptable. I cancelled the booking, they have agreed to refund me the first pmt and promptly continue to deduct further pmts. Refunded me the first pmt, but not the second. Will definitely not be using booking.com soon.