Thanks for posting your concern in our Community. I know how important it is to be able to monitor your camera system effectively.
The Picture/Video storage quota is based on the number of pictures taken per day. It does not take into account if the content is deleted it will only take X amount of pictures/video based on your subscription. If you are finding you are reaching your quota often it may be a good idea to upgrade to a larger quota of 600 videos and 1000 pictures.
If you are only recording from one camera, there is also an option to record locally to the Touchscreen via a 64 GB Class 10 SD card, 24/7 for up to 7 days.