I have successfully solved that issue, First Check your cron job .. I found one cron job running.. which is to download the corrupted file every second. first I deleted that cron job.. then I temporarily suspend the account. because Cpanel run cronjob in memory .. so after deleting the cronjob still the files was created .. so I have suspended the account for a while and removed those two files index.php and .htaccess and then unsuspended the account.. everything back to normal ?? .. Hope that will help you
