php-ext-xlswriter how to get calculated value from cell

all. I use this extension for super fast writing excel file. Example from documentation tell that i can input formula to my file:

$excel = new \Vtiful\Kernel\Excel($config);

$file = $excel->fileName("free.xlsx")
    ->header(['name', 'money']);

for($index = 1; $index < 10; $index++) {
    $file->insertText($index, 0, 'viest');
    $file->insertText($index, 1, 10);
}

$file->insertText(12, 0, "Total");
$file->insertFormula(12, 1, '=SUM(B2:B11)'); // insert formula

$file->output();

But when I trying to read my SUM cell, i getting each time zero:

$data = $excel->openFile('free.xlsx')
            ->openSheet()
            ->getSheetData();

        var_dump($data);

Can anyone advise how i can get calculated value from file? (file only for example, in real task it's bigger much more).