I have two cell phones. I have a Galaxy S9 that is sued for business calls. I have had that phone for over a year without any issues. On that phone:
Cloud storage is disabled
Auto updates are turned off
Data Saver is on (which is supposed to prevent apps from running in the background)
Backup is off
Location is off
Permissions have been denied for any apps I do not use
Bixby was never initiated and to the extent possible, permissions were denied.
Much of the Samsung bloatware has been uninstalled or disabled
There are few added apps: ESPN, two local newspapers and CNN.
The phone came with Chrome and Samsung Internet. I installed Firefox as well (which I used for internet).
I don't stream music or watch video on either phone.
The personal phone is linked to my car via Bluetooth (and so was the old Iphone).
My carrier is Verizon and I have a 4 GB shared data limit. Typically, my data use is under 2GB per month
The phone is mainly used for calls and messages. I am careful to close all apps before sleeping the phone. I do not typically leave WiFI on and only turn it on when I plan to use the internet or download updates.
About a week ago, I purchased a Galaxy S!0 to replace the old IPhone that was used as my personal phone. The set up on this phone is the same as on the GS 9 and is the same as what was on the old Iphone.
Saturday morning at around 2AM, I started getting text messages from Verizon. The first said I had exceeded my data limit and the 2GB carryover from the previous month. This message was followed in rapid succession by 5 others saying 1GB of extra data had been added to may account. I was up to about $100 in additional charges before my brain kicked in and I turned on wifi. That stopped the data bleed. At that time, the phone was not in use and had not been in use much that day except for calls and text messages.
Almost immediately, the text messages started on the business phone. I received two additional data boosts before I could get to that one and turn on wifi. That phone had not been used for several days.
I checked the Verizon website and it showed that 90% of my data use was for Cloud/File transfer. I do not have cloud (it is disabled on both phones) and have backup turned off on both phones.
The individual phones showed that all of the data use was from Firefox running in the background (data saver was supposed to prevent apps from running in the background, but firefox apparently created an exception for itself).
I immediately uninstalled Firefox and the transfers seem to have stopped.
Over a few years, other people have reported similar events online on both Firefox and Chrome. Interestingly enough, the excess data for these reports is 5GB---the same as mine. Firefox has never provided a solution. other than to suggest that the user must have been watching video or streaming music in the background, which the users denied that they were doing.
I do not know what to make of this and would appreciate any input. The thing that is especially puzzling is that the GS9 has had the same setup, apps and usage for over a year without incident. Since it wasn't even being used much, I can't identify anything that would have triggered this. And the new GS 10 simply replaces an old iphone with the same apps, set up and usage.
I am greatly concerned that my phone data went somewhere. Fortunately, there was not much on either phone except perhaps some email and text message exchanges...and maybe a few family photos.
My carrier is not able to provide any help except to tell me how to turn data saver on (It was already on at the time all of this went down so that info is not helpful).