We use Accor quite a lot and am surprised at this. A couple of things we have discovered which might not help your plight directly, but suggests that the relationship with Accor and the hotel can be more distant. Some of the Novotels are directly owned by Accor; others seem to be franchised. Found this out when a franchised hotel was once less generous with its 'welcome drink'! Working the other way, sometimes the hotel itself (Ibis have done this) is more flexible, even with a 'no-refund, no-change' booking, if your plans change when the central reservations are unlikely to be.That's the thing - if I'd gone to an intermediary I'd expect it to be trickier to resolve.
Accor is the owner of the hotel - they have numerous chains under their umbrella.
Each Accor hotel has its own dedicated email address, which you can find on their web site. I'd be tempted to keep going with copies both to the hotel and Accor reservations until they come round. I have had a few issues with them over the years but nothing like this. Usually resolved with refunds, apologies and some additional points on the loyalty card. Bon courage!