Here is North American Power and Gas, LLC website and some contact info. In case you want to let them know your displeasure.
http://www.napower.com/

Customer Service:
Telephone: Toll free at 888.313.9086 or locally at 203.893.4196
Email: customercare@napower.com

Representative Support:
Telephone: 888.313.9086 (option 3) or locally at 203.663.9799
Email: support@napower.com

Advertising & Sponsorship Inquiries:
For sponsorship and advertising inquiries, please contact:
L. Alexander
lalexander@napower.com

Press Inquiries:
Carrie Waible or Sarah Gentsch
Telephone: 212.379.4024
Email: napower@cwandco.com

Corporate Headquarters:
Twenty Glover Avenue
Norwalk, CT 06851
Telephone: 203.939.1155

Careers:
Telephone: 203.939.1155
Email: careers@napower.com

Cursed me and hung up when I asked if they were with my credit card company.

want to know who is this

This is a northern New Jersey number.  Caller ID said "Client Services".

Caller ID said "Client Services", however they left no message and there is nothing on Google for this number.  Hmmm  smells fishy.