How do I contact "Valve" to report Glitched Achievements in Left 4 Dead, Crash Course. Xbox 360?

I'd email there customer service. I did that with a different game, um, Fight Night Round 4 (it was glitching with its multiplayer...couldnt access anything) and I got an email the next day saying it was fixed. Low and behold it was! Mind you this was EA, but I think Valve worships its customers so I would definately give it a shot by emailing them.