The fact you received this notice via an email makes it very suspicious and very likely a scam to extort money from you. You should never respond to unsolicited email. If there was truly a suspicion of illegal copyright infringement going on at your residence, I would expect you'd receive a notice in the mail.
I don't know what you mean by i/p, but I will assume you mean Internet Service Provider (ISP), like CenturyLink, Verizon, etc. The phone number in the email could easily be a fake, and not associated with your ISP.
You could go to the website for your ISP, look up their contact information, and verify that the phone number in the email is legitimate. You might have to call your ISP to verify it's legitimate. If the phone number in the email was fake, it'a certainly a scam. Either way, I would report this to the FBI as a potential scam, because even though the person you called was low pressure, you were left with the threat of current, and increasing fines.
The FBI has a web page (link below) with information on current e-scams, and how to report them. If you read the page, you will see that many of the scams described involve telling someone that their IP address has been involved with accessing illegal content. This is exactly your situation.
http://www.fbi.gov/scams-safety/e-scams
You report a potential e-scam via this webpage:
Internet Crime Complaint Center (IC3) | File a Complaint