On their site: "upgrade to an FNB corporate platinum credit card"
Usage of "a" or "an" is determined by the pronounciation of certain words
“No one can make you feel inferior without your consent.” — Eleanor Roosevelt
Oh, ABSA is guilty of much more than just bad grammar !!
"An" is used before a "vowel sounding" word and not just a vowel. Which is why you'll notice Americans using it for some "H" words.