Session not unset as I unchecked checkbox

Here, When I going to unchecked checkbox, session is not unset. The value is stored in session but when I am going to uncheck, the unset is not happening. Where am I stuck? My code is, for checkall and uncheck all,

function CheckAll()
{
    var frm = document.order;
    var checkboxobj = document.getElementsByName("id[]");

    if(frm.checkall.checked)
    {
        for(i=0;i<checkboxobj.length;i++)
        {
            var val = checkboxobj[i].value;
            $.ajax({
                     type: "GET",
                     url: "view_orders_checked_array.php",
                     data: {account: val, task: 'add'}

                 });
            checkboxobj[i].checked = true;

        }

    }
    else
    {
        for(i=0;i<checkboxobj.length;i++)
        {
            var val = checkboxobj[i].value;
            $.ajax({
                    type: "GET",
                    url: "view_orders_checked_array.php",
                    data: {account: val, task: 'remove'}

                });
                checkboxobj[i].checked = false;

        }
    }
}

The session code for my checkbox is,

require_once 'includes/config.php';

$account = $_GET['account'];
$task = $_GET['task'];

if($task == "add")
{
    if (!isset($_SESSION['id'])) 
    {
        $_SESSION['id'] = array();

    }
   array_push($_SESSION['id'], $account);
}

else 
{
    //unset($_SESSION['sms_id'][$account]);
    if (($key = array_search($account, $_SESSION['id'])) !== false) 
    {
        unset($_SESSION['id'][$key]);
    }
}
print_r($_SESSION['id']);