If your cell phone sees LTE but can't make or receive calls reliably, the LTE service from the Operator might be having an issue where you are located (this is not a Cel-Fi issue). Try disabling LTE and see if call reliability improves. You can always turn LTE back on, or even get an LTE ON/OFF widget App to simplify things.
How to disable LTE:
iPhone users simply tap the “Settings” icon, then tap “Cellular”, then tap “Enable LTE” to move the slider button to the left (LTE disabled mode). To re-enable LTE, simply tap “Enable LTE” to move the slider button to the right/green (LTE enabled mode).
Android users can download a “LTE 4G switch app” compatible with their device from the Google Play store; OR try Settings>More Networks>Mobile Networks to disable LTE; OR the user can perform the following manual steps for disabling/re-enabling LTE (instructions might differ slightly on different devices):
- Tap the “phone” icon to display the dialer window
- Dial *#*#4636#*#* on the phone; the phone display then opens the “Testing” options window. Be careful not to change other settings in this menu!
- Tap the “Device information” or "Phone Info" option; the phone then displays a long list of device settings
- Look under "Preferred Network Type" or Scroll down the list and tap the selection entitled “LTE/GSM auto (PRL)” to display cellular options
- Tap the “GSM/CDMA auto (PRL)” option to select it
- Tap the Android back-button 3 times to return back to the home screen
- “4G” or “3G” should now be displayed in the status bar at the top of the screen, indicating LTE cellular service is disabled.
- To re-enable LTE cellular service, reverse the process and select the service option that includes LTE.