If the email did not come from someone specified as legal council from wherever it came, and it did not mention specifics on exactly copyright infringing you supposedly did (specific title/software names) - tell them to stop uttering threats and wasting your time.
Looks like a troll to me. No company in their right mind would send such a thing without providing more information directly from their legal reps.
Ask them to mail you the proper and specific paperwork like they should have to start with if they believe you are infringing on their assets.
