If you're paying your bills on a monthly basis by direct debit, then you'll receive your statements every six months. As you have paperless bills, we'll email you when your statement is ready to view. It could be that your statement is simply not due yet.
You can check when your next statement is due in "My npower" by signing up using the following link: www.npower.com/At_home/Forms2/MyNpower/Benefits.aspx.
If you think you should have received your statement by now, please contact customer services www.npower.com/web/At_home/customer_service/contact_us/customer_enquiry/index.htm or call 0845 166 3443 and they can check this out for you asap.