I'd file it as a concern and also send it through to IHG Care asking for it to be escalated immediately as well as emailing the revenue manager above.
I'd be looking for points to the equivalent of a free night at a similar property for the BRG, full refund and further points to equivalent of a free night at this property for the rank incompetence that has been demonstrated.
That and the General Manager on the phone pronto to explain what kind of show he is running here.
It's just a pity you arrived in the middle of the night, hopefully you get this sorted.