Sorry to hear you have to go through this. Everytime I had to deal with ALL Customer Service it has been a useless nightmare and I made multiple suggestions that a very much welcome perk of higher statuses would be a damn responsive, capable support. You mean Accor Plus as in their APAC program, right? Not the weirdly named ALL Plus card? The fact that you have an Accor Plus makes it even harder because as far as I understand your support requests get routed back and forth between "normal customer support" and the APAC team that handles Accor Plus guests.
Have you tried Accor Plus chat? They can arrange callbacks so maybe it helps.
As for getting the price honoured I truly doubt it but nothing lost in trying — do you have screenshot of that pricing? — I'd perhaps even try to email the property vs. Accor CS.