Send email after 7 days if status is always "pending"

Question

I need help or an explanation to send an email once, to people who do not pay bank transfer or bank check (status pending) after 7 days.

Example: A customer orders today by bank transfer. If after 7 days I still have not received the transfer, I send one and only one email to the customer to restart the payment.

How can I do this?

I create a custom module with cron job and observer and helper: This is my cronjob :

<crontab>
    <jobs>            
        <custom_standbypayement>
            <schedule>
                <cron_expr>*/1 * * * *</cron_expr>
            </schedule>
            <run>
                <model>custom_standbypayement/observer::checks</model>
            </run>
        </custom_standbypayement>
    </jobs>
</crontab>

My Observer :

public function checks() {

   // $arrayEmail = Mage::helper('standbypayement/data')->cancelPendingOrders(); 
    $arrayEmailEmpty = Mage::helper('standbypayement/data')->cancelPendingOrders(); 

}

this is my helper who gets all order with state pending and sends email transactional

public function getPayementBankTransfertStandBy(){


    $olderThan = 7; //7 days
    $date = date('Y-m-d', mktime(0,0,0, date('m'), date('d') + $olderThan, date('Y')));

    var_dump($date) .'</br>';     

    //get orders with no update in the last 7 days
    $collection = Mage::getModel('sales/order')->getCollection()
                ->addFieldToFilter('status', 'pending')
                ->addFieldToFilter('updated_at', array('lt'=>$date)); 


    return $collection;


}
public function cancelPendingOrders() {

    $arrayEmail = array();

    foreach ($this->getPayementBankTransfertStandBy() as $order) {

        echo $order->getIncrementId() .' - '. $order->getCreatedAt() .'</br>';     
        $arrayEmail[] = $order;
        $this->StandByPayement($order);    
    }

    return $arrayEmail;

}
 public function StandByPayement($order) {
    $storeId         = Mage::app()->getStore()->getId();
    $email           = $order->getCustomerEmail();

    $senderName      = Mage::getStoreConfig('trans_email/ident_support/name');  
    $senderEmail     = Mage::getStoreConfig('trans_email/ident_support/email');  
    $sender          = array('name' => $senderName,
                             'email' => $senderEmail);
    $paymentBlock = Mage::helper('payment')->getInfoBlock($order->getPayment())
        ->setIsSecureMode(true);

    $paymentBlock->getMethod()->setStore($storeId);

    $paymentBlockHtml = $paymentBlock->toHtml();

    $vars       =   array(
        'order'        => $order,
        'billing'      => $order->getBillingAddress(),
        'payment_html' => $paymentBlockHtml
    );


    //var_dump($vars);
    //die();

    $templateIdEn          = 55;
    $templateIdDeutsch     = 56; 

    $translate       = Mage::getModel('core/email_template');

    $translate->sendTransactional($templateIdEn, $sender, $email,'', $vars, $storeId);

}

Can you help me? I want to send just once email if the status of payment is always pending after the day of purchase

Thank you