Unauthorized tethering accusation
I just got a nasty email from AT&T about the use of my iPhone 5S, running iOS 7.1.2. I have an unlimited data plan. I have been an AT&T mobile service user for at least three years and I got my iPhone 5S, nearly a year ago. The email said I am using tethering without authorization and that I may need to be changed to a more expensive data plan if I don't stop. The trouble is, I am not using tethering, nor have I ever used that feature. I checked my iPhone's settings and it is off. I called AT&T and they said an app might be turning it on, but they couldn't provide any details. I also rarely drive and my car does not have bluetooth capability. The only bluetooth accessory I ever use is synching with my Fitbit Flex, which I have had for at least the past six month. How could could AT&T claim I use tethering when it is disabled on my iPhone and my app usage pattern hasn't changed in ages? I don't use any high bandwidth apps, such as NetFlix. The iOS apps I use the most are: Mail, Facebook, Twitter, Safari, Foursquare, Fitbit, iTunes (to listen to pre-downloaded music), the Camera app, Words with Friends, and the New York Times app. So how can I make sure no app on my iPhone uses tethering if apps can turn that feature on without my knowledge?
If anyone can help me get to the bottom of this situation, please let me know. Googling has not helped.
iPhone 5, iOS 6.1.4