Those prices are f***ing awful! - the ones on here will be their online discount tariffs (the most competitive section of the energy market is online tariffs, you will almost always secure the best deal online)

consumer direct are my advice, you need help and time to review the bill. They should not have sent collections onto you without giving you a chance to dispute the bill first. Have you checked the readings they are using against your own move in readings? Have they got the correct meter serial number on the bills as matches your meter?

http://www.consumerdirect.gov.uk/

Let me know..

G