function add_content_specific_email( $order, $sent_to_admin, $plain_text, $email ) {
$payment_method = $order->payment_method;
if ( $payment_method == 'bacs' ) {
echo 'Your text';
}
}
add_action( 'woocommerce_email_before_order_table', 'add_content_specific_email', 20, 4 );
