I think that their email provider put it in the JUNK (ie. spam) folder. That's happened to me a few times with Gmail. More than once I haven't received a response from a company, and when I call to follow up I get "Oh, you have Gmail? Let me check the JUNK folder. Oh yeah, here it is."

I wouldn't get worked up about it. I'm sure that they don't think you are junk.