
Quoting
cdwjava
You'd have to ask your ISP what they mean by that. I suspect it means that they received the subpoena from a law enforcement agency.
Law enforcement is not going to be investigating civil matters. To utilize a subpoena, a criminal investigation must exist. However! That does not mean your IP is a suspect in this, it might be meant to identify other victims or potential witnesses of someone else's activity that crossed your path.
Unless you want to go to court and see if a court will compel the ISP to provide a copy of the subpoena, about all you can do is ask.