I am using a D-Link wi-fi cam and it *appears* to be using 10GB a day. This cam IS NOT set to constantly send recordings to the cloud. It is not being monitored all the time. It is not even recording...
Relatively speaking, HD (720 or 1080) uses 1-3 GB per hour and 10 GB per 24 hours would be about 450 MB per hour. 450 MB per hour is equivalent to streaming very low-quality video (240 or 320). I'm not saying this is the video format but the equivalent data rate of 10 GB per day.
I think your app points to a server on the Internet. When you use the app, you're not logging into the camera but into a D-Link server. Although you're not constantly recording, streaming or using the app, the camera(s) must send something to the server to keep your service (connection & app) "alive" 24/7.
I don't know what the camera is sending...perhaps an image every hour or an image after a massive change in pixels...but it's the cost of a web-based service.
widermouthopen is correct: You need to ask on the D-Link Forum to configure your camera to only transmit data when you're logged into the app...if possible.
Thanks for the feedback, It has been helpful. But, the mystery is still there. As far as I can see in my settings, I am not sending anything back over the internet, i.e., no cloud storage. I would think the only time data would be used is when I log in to view what the camera is pointed at, and I do that very rarely. BTW, I have security software on my router that shows all connected devices and warns of any attempts to connect from outside sources and nothing has been detected. I also turned the camera off 2 days ago and again the data usage dropped significantly.