Did you have an abnormal amount of toilet flushes or something?  Not being silly, just trying to help find the cause.  We had a couple HUGE water bills over the summer, like tens of thousands of gallons of water "usage" that died down since. 

We didn't even both to contact them - because we assumed the response would be what you heard.  How could a utility be incorrect about something?  LOL.  They sent us a late notice in the mail, it arrived 1 day after we got our "convenient" online bill via Email.  It's quite an annoying utility.  GCEC electric on the other hand - we LOVE them!  And they billed us our neighbor's usage for 5 months.  They finally got it sorted out (with our assistance and persistence).  But I highly doubt the water folks will be the same way.

I noticed my water bill was $100.00 more than it usually is, no watering the garden or lawn, so I made note to look at it again next month, thought maybe the kids did some extra laundry and gosh knows they love to take showers that seem to last forever, but I received a call today from the water department, she said my meter was misread and that I had a $99.00 credit. It is possible they made a mistake!!!!

This happened to us about a month ago.  My water bill was $200 more than usual.  They said I had to have a leak.  Funny thing was, the next bill was normal.  I've never heard of a leak that fixed itself.  We didn't have any leaks, running toilets, we did the same amount of laundry.  We asked if it was misread, and they said no, and it would cost $50 to come out and check the meter.  We ended up having to pay the extra $200.  Sure would be nice if they come back and say it was a mistake on their part.  :-)