Guys,
You can go ahead and raise RBI ombudsman complains , error quotes or prices are common, it's on the vendor whether to respect those error prices or reject it.
Your RBI ombudsman complaints would mostly get closed as Amex has already sent an apology regarding the miscommunication.
Not defending Amex or anyone here, there have been cases where HDFC or axis has displayed wrong pricing or absurd TNC's. It's a tech issue.
So I would suggest don't waste your time on this. Amex doesn't budge to this things much.