Ok, checks logging on to cPanel, but for now run a daily cron job on:
DEFINE( 'DAY' , 60*60*24 ) ;
DEFINE( 'WARNING_DATE' , 12 );
$last_login = filectime( '/home/YOUR_USERNAME/.lastlogin' ) ;
$now = time() ;
$diff = $now - $last_login ;
$days_since = ceil( $diff / DAY ) ;
if(...