This is essentially the response I got from Valve about 4 years ago when I was banned. I spent about a month struggling to get in contact with them just to ask 'why' and 'are you sure.' It wasn't until I began leaving daily voicemail messages at their offices asking for help that they finally talked to me at all. The only thing they told me in that conversation was that the ban offence was at my home IP, so I knew my account wasn't compromised. They even ignored a BBB complaint I filed.

They insisted that their automated ban system could not make a mistake. While I realize that most people banned from any online service probably deserve it, you can tell the quality of a company by the way they handle the mistakes. And there are always mistakes.

Here's where I documented all I tried to do years ago with no success in case anyone is interested: https://sites.google.com/site/vacban/