the problem- celular reception
the problem here lies in cellular reception. radio waves are susceptible to interference and congestion, particularly in busy areas during busy times. loss of an ip connection due to both is common.
Due to the design of network infrastructure, devices do not report their usage according to the device data counters (hex / binary ticker that counts packets in and out of the device), Cellular companies monitor data served and received.
Therefore in an instance where you have a congested network and a loss of ip connection occurs, or if an app requests data by way of process, it may be served by your mobile data provider repeatedly, even if your phone only recieves it once.
Say, streamed video, 300 meg file you hit, you may have had 410-700 meg sent to your cellular ip address even though you only get 300 meg of practical data.
Believe it or not you are billed on the 410-700 theoretical transmission, not the volume you recieved.
If your ip connection is spotty, or you are in a congested area, or you network hop a lot, your'e probably susceptible to the same problem.
Networks won't admit it cause it means they are liable.
The Wifi-Cellular cock of on ios is a different issue. Above refers to cell data, and erroneous cellular only reporting.