Were you able to sort this out? I had a similar thing happen, thankfully for much smaller amount. Booked as cat 2 off peak, hotel changed categories and charged me cat 3 standard rate after checkout....of course I have no emails with the confirmations as I booked 3 months ahead of stay. Tried calling cs, contacting property, messaging on fb, all responses are the new Marriott standard where basically it is my own fault somehow.....I tried lurker as last chance to save that 7500 points but we will see....