No problem, glad I could help.
One thing I forgot to mention you should change any passwords that you have to use to edit and upload your pages, to a one that is stronger (a mix of alpha, numeric characters at least 8 characters and preferably longer). This may help, but if there is a vulnerability in the hosting software (old version, etc. that could be how it is hacking pages).
Perhaps time to start looking for a new Host, whilst things are calm and you know the kind of questions you need to ask of a potential Host, based on your experiences in this case.
Since the index.htm/html page is the first that many arrive at that would be the most efficient method to reach the majority of visitors. There is also a sneaky one doing the rounds where if there is a custom error 404 page (displayed when there is a page not found error) that has been hacked in some attacks.
Welcome to the forums.