Who I have the same questioned this topic

We have a Fusion device with Cantennea for our internet connection. Only have 20 GB or data per month. We have a timer on the Fusion device that goes off at 11pm and comes back on at 6 am. There is no reception for any data during that time.   Plus, we always  break the connection between our coumputers and the WiFI in the house when we log off.  However, on several occasions between 1 GB and 1.9 GB has been logged against our puny total  between 11 pm and  6 am.  This last billing period, that totaled 6 GB of our meager 20 GB. What the heck is going on with this? Seems like robbery to me!!!!  Any thoughts about this? Does this happen to you?