I just got a bundle of letters from my ISP, Charter Communications, for the exact same thing. I didn't even know the damned series was licensed, otherwise I wouldn't have grabbed it either. After just re-checking the letters, seems its Media Factory that's got it licensed. Kinda strange the first thing the community would hear about it is this, not some big torrent site (like BU) posting up about getting C and Ds.
And since the company itself got wind and then sent word to the ISPs, isn't there technically a violation of privacy somewhere in the mix? Shaky legal ground when one is downloading fansubs, I know, but still. I know I'm not particularly keen on my ISP letting my personal info stuff getting leaked hither and lo.