This is definitely wrong and, unfortunately, you dealt with the crappy Accor CS. Could it be that the hotel has decided to opt out of the SNU system and have re-credited the SNU on your account and now ask you to pay in cash the equivalent of the SNU ? Instead of dealing with CS, did you try to solve this with the hotel ? At least, they should give you the non-suite room before SNU and without asking any money.
This has never happened to me.