You cannot reapply to the scheme for 12 months if you have been turned down at any stage, regardless of the letter you receive. If that's it then sadly that's it. Maybe the info you've been getting is made up, exagerated, or for extremely special circumstances, although rumour has it that that the rules aren't bent unless there is a really, really good reason to.
The BA staff will keep your application on file and will review it when you reapply, so if you hassle them them maybe thet'll keep your hassling letters, which is probably not a good thing. Mary Brown is high in recruitment but just so you know she is not the flight crew head honcho in charge of the scheme, incase you were hoping for that person.
Good Luck to you anyway,
SB