Notify them that they're full of crap and you want them to prove that you were sharing these files (which you obviously weren't). Furthermore, you want them to prove that these files were actually copyrighted material. A file name means nothing. What's in a name?
They're trying to scare you and bully you to quit using file sharing services.
You could even tell them that these were all fakes that you were sharing in order to help them and hinder the use of file sharing services. Then they'd really feel like bassholes. How can they prove otherwise? Oh yeah, they CAN'T!