Has anyone seen this issue? Seems even though I've only been using wifi the phone sometimes connects to a carrier and (I'm assuming) using cell data since it's claiming under useage that I've used 23 gb of data.
If Cellular data is off, you will still see the carrier name, but 3G/4G/LTE icon will disappear. If cellular data is completely disabled, it will not use cellular data at all. The 23GB of cellular is probably the life of your phone and if you have used a backup going from iPhone to iPhone, that number never resets. I have an iPhone 4 with a backup that was on a 3GS and a 3G so it says my lifetime data is over 100GB, but its really probably closer to 30GB for that particular phone.
Even when you turn cellular data off, the phone is still active on the cellular network so the carrier name will remain regardless. There's no way to make it disappear regardless of the settings unless you're in airplane mode.
The only way to verify cellular data is truly disconnected, as stated above, reset your stats in the menu and monitor it.