Sadly contacting Steam is very difficult and there is no direct way to contact them. Also regardless of what happens I'm certain Steam will do nothing for me as their return policy is clear. It pretty much boils down to "Too bad so sad" while they roll in money.
Steam can be contacted by raising a support ticket through their website. Not that there's much point since their responses tend to be unsatisfactory. For example, I've just had to submit a case to our local Trading Standards office due to Steam's "no refunds under any circumstances" policy: I had the digital equivalent of a shrink-wrap EULA sprung on me in the form of Ubisoft's infamous DRM scheme lurking in the post-sale terms & conditions, which I unsurprisingly didn't accept. Steam's attitude is "tough luck, loser". It remains to be seen if I'll get anywhere, but I prefer not to do business with companies that'll only offer at best the legal minimum protection.
Larian have tended to be far nicer to deal with in my experience. If they haven't replied to your initial email I'd just send them a polite reminder: that's all it took last time I seemed to have been overlooked.
