I cant figure why usage keeps going up each month.

I keep adding and then dropping down my plan for internet. I cant figure what is causing an increase each month. I get the netfix streaming ect. But is there anything that causes it to count against the plan that I am over looking? If anything is plugged in but not used,like google hub,is that only charged when asked or using it? Will anyone in neighborhood connecting make it go up. I know at times with friends and family over everyone has the phone on ect ect, Help me understand maybe something I am not seeing. Thank You