This is terrible and so unprofessional! A similar thing happened to me last year (not at such short notice, though) when Mercure Vienna Josefshof decided to leave Accor and I had a stay booked with them. I too had paid part of the rate with reward points, which they credited back to my account and made me pay instead. However, they were completely professional and gave me the room upgrade and welcome drinks and even managed to credit the status and reward points I would have received, through another Accor hotel in Vienna. So everything worked out well in the end. Maybe you should demand that the hotel shows you the same courtesy. Especially given that you're a Platinum member.