There's no perfect way to describe the relationship between Marriott and their hotels but I think the best way to describe Marriott as a booking agent. A hotel is sent the bookings made for their hotel, and they can modify some information which is pushed back to the Marriott system. The Marriott customer service team on the other hand have direct access to the Marriott booking system, and they can manage bookings across all hotels, and diagnose account issues. So, in this case, there is most likely an issue with your account or bookings in the context of the Marriott booking system which is also present in the booking information Marriott have sent to the hotel. The hotel, most likely, didn't have full access to your broken booking, and so they've cancelled the only booking they're able to.

As a general rule, any support request that relates to booking through the Marriott website or app should go to Marriott customer service, and any support request that relates to staying at the hotel should go to the hotel. So, roughly, before check in = Marriott customer service, after check in = hotel.