Are you sure it’s the Steam anti-cheat that got you banned? If you’re getting an in-game message that you’ve been banned from accessing official servers, then Funcom banned you for breaking the rules of their Official Server ToS and you need to open a Zendesk ticket to ask them for more information. (Make sure you pick the correct value for the request type field.)
If you’re getting a different message, you’ll need to describe it (or even better, attach a screenshot), so someone can figure out what’s going on.