Samsung Galaxy Tab S 10.5
We have found 2 possible solutions to your problem.
Before you start this troubleshooting guide you need to check one important thing:
Can you make a voice call?
Yes
No
Why do we ask this question?
Why do we ask this question?
If you can't make a voice call you need to solve this problem first. Solving this problem will most likely also solve your problem with using tethering.