There was a similar issue brought to light on this forum recently. I came down to the fact that apparently there was a new person reading the meter and screwed it up. I can't say that's what is happening here, but I will say that it is virtually impossible for the water usage to jump that much. I don't care if the every toilet in all of the houses were not shutting off and the yard hoses left on 24/7. If the city continues to stonewall you, contact an attorney.