Data Consumption on Static IP

Data Consumption on Static IP

I don't have much idea whether it is the right forum for these sort of
questions but i need some help, would be thankful if someone give me the
idea for this.
We've a wireless internet connection in our office and the day since then
our office has switched from a dynamic IP to a static IP, the data
consumption has increased more than doubled.
We have a 20 GB monthly limit but do not have any internet consumption at
our office except the emails we receive and the anti-virus or software
updates. The only thing we do is to connect the software on the machine
via remote desktop (as we have 2 office locations), which i don't think,
could be a cause of excessive usage.
We have even put a restriction recently so that only the IPs (which we
have added in our modem firmware) could connect to the internet, but
within a week we have got a notice from the provider that we have exceeded
our 50% data consumption limit.
Any ideas?