Originally Posted by Ditto

While I'm glad that quoting the DOT rules helped you getting back what you shouldn't have been charged in the first place it remains irrelevant as you seem to have been sold a "light-fare" ticket which included 0 checked-in luggage and your luggage allowance is based upon you being an STE.

Unless by some weird way AF sold you a ticket with different luggage allowance for the outbound and the inbound portion, e.g. a standard fare going to MLA but a light fare going back, but I very highly doubt that.