IANAL, but I'm pretty sure you can't copyright a word. Trademark, on the other hand, definitely. I'm inclined to think that this is just a standard C&D. It's just that the two concepts get confused a lot, and copyright is easy to abuse (since it's always assumed to be a valid claim—which works in the hands of individuals, but is outright unethically used in the hands of corporations). If you filed a counter claim, I doubt they'd even pursue it. :\ But still, it sucks hardcore.