the url for the cron job was something like that : https//www.mywebsite.com/acynamefile.php
and the code is :
<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,'https://www.mywebsite.com/index.php?option=com_acymailing&ctrl=cron');
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
@curl_setopt($ch, CURLOPT_FOLLOWLOCATION,true);
curl_setopt($ch, CURLOPT_AUTOREFERER,true);
echo curl_exec($ch);
curl_close($ch);
?>
But I can't test this file because in the configuration I can't change the cron url to my mine