First, check your credit report to see if it is listed, if so, contact the company directly (not using contact information in the email -- Assume the email is a phishing attempt)
If you talk to them be sure to indicate you're willing to pay but request they provide everything in writing, including proof of the outstanding debt, final bills, etc.
If it is on your credit report, also request proof of what steps they have taken to try to contact you before reporting, while also disputing it with the credit reporting agency.
If it isn't on your credit report, and if your physical address hasn't changed, then it's a phish and can stay in the junk folder unless it has specifics like your account number (and even then, be wary).
Regardless, be cautious, and keep in mind that phishing attempts often try to freak you out a bit (giant bill, making threats if you don't take immediate action).
Or just contact them and offer to pay in iTunes cards (half joking, but if it is a scam they might just jump at this while no legitimate agency would even consider it).
