Hi Kristof,

Please send listing of your main (root) directory. Ist there any other index.html in your main directory (not allowed)?

FAQ by 000webhost.com:

If you want site visitors to be able viewing and accessing files, all files must be uploaded to public_html directory. You may create other sub-directories inside public_html directory if needed.

Files uploaded outside public_html folder will not be accessible for your site visitors. Your site will not function, if there is no public_html folder, so, if you accidentally deleted it, please use Fix File Permissions tool from control panel and it will restore your public_html folder.