How to clear INDEX OF from my webpage

Am new to web design and cpanel generally On Saturday 25/2/2017, I edited my site, changed the css and html file names, then refreshed the page and what I saw was INDEX OF(picture attached) instead of the main web page. The site was okay before the edit. On Sunday, I emailed the hosting company to 1.reset my domain to default and delete all files and folders, and if possible too 2. transfer my domain to another server. I don't know if they also carried out option 2, but I noticed the files were no more, so I believe the domain was refreshed(option 1). But on uploading the files again with the instruction they sent me, I still noticed the INDEX OF/ and that's what is still showing when anybody accesses the site. Before, I could access my files using the FTP software Filezilla, but now, it throws an error thus: FAILED TO RETRIEVE DIRECTORY LISTING. Please what can I do to clear this, cos my hosting company don't seem to get it right, thanks. Sorry I didn't provide an option to watch the thread in the first I submitted.