Sorry, "ma'am" is the common and polite form here ("sir" for males.) It's less common to call a lady "madam", and please keep in mind that "madam" also means the female manager of a brothel. Also, the correct way of addressing Queen Elizabeth II of England is "ma'am" (although it's pronounced "mahm").

I believe that in english anything with an apostrophe is less polite. Original english does not use contracted forms as much as modern english does. 'It is' is more polite than 'it's' 'Does not' is more polite than 'doesn't' 'Is not' is more polite than 'isn't' 'Going to' is more polite than 'gonna' etc...

madam is more formal.