Booking.com is charging me GST

They are threatening to put me in collections for not paying GST invoices. I pay my taxes to my government! ... I have an accountant who handles my taxes. My lawyer and the government both say this is nonsense. I gave them my business number. Told them I have an accountant who will use ITC and is paid to handle my taxes Not booking.com. How dare they hold onto my money. I always paid my invoices. They do not charge any other accomodation in my area GST! Why single my property out?! Makes no sense. Cannot get their finance department. In the phone and they just keep sending threatening emails about collections and ruining my credit rating. Wow!!! 
so mad right now