Similar thing happened to me many years ago, except I wasn't applying for promotion I was applying to go back into the position I had held before leaving (a mere 12 weeks before). I just bit my tongue and accepted what they said.
However, the same position came up at another at the same time and I rang the base stewardess to be met with the comment "of course you can apply, you're already an IFS aren't you ?". I got the promotion ....