Got a similar bill from the electric company one time
They had changed my meter out (the new one starting at "0"), but forgot to reset the counter on my account to 0, so it had calculated that I used enough juice to flip the counter and I had a bill for $25,000 or something crazy like that.
"I believe there is a problem with my account..."
"What is your account number, sir?"
-provided-
".....oh....I see....It looks like you're our best customer, so what's the problem?"
(yes, she was joking)