OK Here are a few things to check. If you duplicate the Home (index) page and do not rename it, I think it gets renamed index-1. Duplicate the page again and it gets renamed index-2. So check the Page & Layout Gallery and make sure this is not happening. If you have an About Us page, for example, change the page name to about-us.

Make sure you publish the whole site, even if you have only made changes to one page.

Browsers automatically look to see if there is an index file if all you key in is the domain name, e.g. mysite.com If the browser finds two index files, index.htm and index.html it will load the .html file, even if the .htm file is newer.