Great you contacted Accor CS and the hotel and have it all documented.
For the correct number of nights on a simple stay to post correctly, very, very basic issue, it has been dragging for over four months, thus I would contact Consumer Protection on your country where Accor surely have properties. Do not hold your breath on Accor CS or the hotel and make them aware that legal actions are being made.
To put it simply Accor CS simply fowards your request to Hotel and wait, until Hotel sorts the issue out. In my case, they have been waiting for 4 months... and they have no hurry, as it seems, even if it is such a simple issue. Just imagine your case.