Replying to BitTorrent Tracking

So...today I got a letter from Comcast sent to my house threatening to end my families subscription for TV, Internet and whatnot. They said that they have tracked illegal movies that I have downloaded, such as Animal House. They said that Animal House was the movie that they tracked and I was just wondering how I can avoid this or if I should stop all together. I usually download the files, save them to iTunes, etc., then delete them from BitTorrent for that very reason. Can they track it if I do that? Animal House was left in my BitTorrent queue for about 3 weeks just because I forgot to delete it.