Nicor Gas did the exact same thing to me in 2007 - I received no bills, no one came to read the meter, and I couldn't get a coherent explanation of why for almost a year. Then I received a bill for over $700, with only an offer of a payment plan.
Today, I get a bill from Nicor for over $1100, even though I have paid any and all bills on-time. Their explanation is that they had noaccess t0 read my meter for 8 months (no one came out to read the meter, and the online meter-reading application would not accept the entries I made), and when they finally sent out a person in March and May, that lead them to determine that they had underbilled me for over a year. I work from home, and I have dogs that bark when anyone steps onto my property, so I KNOW that no one has been sent here to read my meter, and when they DO come, they have access.
Again, no real explanation and an offer of a payment plan. If anyone knows to whom we should complain, please post that information. Thanks.