Any experience with this outside of the US and based on Smoking versus non-Smoking room types?

I am booked in for a 5 nights stay in Asia over the New Year period at a property (St Regis) that looks to be well and truly sold out. I booked a basic deluxe room and although I'm a Plat Prem I am not expecting an upgrade on the room class given the property is full. I did however book a non-smoking room, something that is confirmed in the email booking confirmation I received and that's absolutely something I would expect to be honored.

I am now looking at my booking on the MR site and it says 'Unavailable: non-smoking room'

Is there a room type guarantee I can invoke to prevent them from moving me to a smoking room? I really really don't want to be stuck in a smoking room for 5 nights (allergies) however trying to rebook at this short notice to another property is more or less impossible unless I want to spend an absolute fortune (I don't!)

Anyone been in the same situation?