I don't know ... this is a tough one since the the responsibility of error is shared. Looks like Brooks Brothers employee gave the incorrect size information (or gave the right size but sometimes different brands fit differently) but OP also failed to try on the suit before having it altered. I think if OP were to take some time and write a letter to both AmEx as well as Brooks Brothers, perhaps some goodwill gesture can arise out of one or both of them. But IMO that's all what is owed ... a goodwill gesture.