@Ghany
Look, if you place into PHP file code:
<?php echo 'It works'; ?>
You eliminate any programming errors, it is easiest PHP code and you can be sure everything is OK in this file, it is not related to anything, it only show text.
If you still cannot open this file and getting Internal Server Error, there is problem on your server accessing this file and if your hosting provider tells something like this, he is doing idiot from you.
Even more, they should be able to tell you exactly what is problem. I can tell you experience with my hosting provider, there was problem that on prestashop paypal payments could not go through and users could not buy anything. You can be sure that such error can be done only by expert in this area. They have identified issue, fixed it on their servers and were tracking my payments for next 2 weeks to make sure everything is going ok. For 30€ per year.