Did you look at the details of the bill opposed to just the front page?
We don't have access to accounts here. Open up the bill and go to page 3. That usually is the Account Details section of the bill and it will explain why the bill is what it is.
The extra amount could be overages, late charges, data use, NSF fees for not having money on the credit card or bank account if you have preauthorized payments set up, reconnection fees if the line was suspended.