Funds are taken by Direct Debit after your AAdvantage® Debit Card transaction has taken place. Some banks assume that Direct Debits recur monthly, and so they can incorrectly predict upcoming payments based on the latest Card payment.
As an example, if you made a £50 transaction on 5th March with your AAdvantage® Debit Card, your bank may incorrectly predict you will have another £50 transaction on 5th April.
You should ignore this - the money will not come out as it is an error with your bank. Please do not cancel your Direct Debit as this will impact future usage of your AAdvantage® Debit Card.