Samsung Galaxy S4 - No sound during 4G calls and no ringing for connection

[AC Question]

This is apparently a fairly widespread problem, but I'm having a lot of trouble finding any solves.
When I am trying to make a call over 4G or to receive a call the same way, there is no sound going out or coming in. When I am making the call, the little music of connection happens, but there is no ringing following.
I've gone through all of the other sovles that I could find so far. I actually did a reset of the phone (and had to put all of my stuff back again. bummer.) That worked for a week or so but here we are again. I've disabled all of the bloatware I could find. I do not have OK Google or any of the Google voice programs installed, I don't use Bluetooth, and Svoice is disabled. I turned off GoogleDrive. All of my ports are clean enough and functional. I're restarted and pulled/replaced the battery/SD/SIM many times. (This works on and off for a call or two.)
Calls DO work over WIFI and do NOT work in SafeMode.
My dread would be that its the SIM reader and has to take my phone out of my use for over a week. My annoyance would be that its a firmware thing that has no solution at all and has been ignored by Samsung.
Anyway.
Has anyone got any suggestions or thoughts? Appreciate it greatly.

 

[B. Diddy]

Welcome to Android Central! Is VoLTE (aka HD Voice, Advanced Calling, or Enhanced 4G) turned on?

 

[ravingglowstick]

Welcome to Android Central! Is VoLTE (aka HD Voice, Advanced Calling, or Enhanced 4G) turned on?

I don't even seem to have the options for any of those, so no, not turned on.

 

[B. Diddy]

How do you know the calls are 4G calls? That would imply it's a VoLTE (Voice over LTE) call, and the phone has to support that. If you don't see any of those abovementioned options, then it's not likely that the phone supports VoLTE. This means all calls would be going through 2G (GSM or CDMA, depending on your carrier). If that signal is poor, that might be why you're not getting calls. The signal bars you're seeing in the status bar probably represent 4G LTE, which may be different from the 2G signal. So even though you have decent LTE bars, it's possible your voice signal isn't good enough.