First off, start using some basic data structures.

my %sheets;
$sheets{$_} = $workbook->add_worksheet($_)
    for qw( AP NAP );

my %column_headings = (
    AP => [qw(
        Login UserName Group ...
    )],
    NAP => [qw(
        Login UserName LDAP-Status ...
    )],
);

foreach my $sheet_name (keys %column_headings)
{
    my $col = 0;
    foreach my $col_name (@{$column_headings{$sheet_name}})
    {
        $sheets{$sheet_name}->write(0, $col++, $col_name, $heading_for
+mat);
    }
}
[download]

If you do that, especially using the (row, col) addressing vs. the 'A1' addressing, you'll be a lot better.

Of course, you could just stop using Spreadsheet::WriteExcel directly and use Excel::Template instead. (That's what I'd do ...)