During an 8-hour flight in Business class, I called the flight attendant "Ma'am" to get her attention. My husband then told me that I should not have called her "Ma'am" since I am the "the ma'am" (the customer). Is he right?
Ma'am is not an entitlement, it is a polite way to address any adult female. Your husband was wrong, as both you and cabin attendant can use the term.
And contrary to some of the younger responders is not an outdated term, as it is in common usage still in many parts of the English speaking world, except maybe the connected generation where politeness has been forgotten.