Select   Set preferred Network Type:

 

Select   LTE only or other option

 

Remember on some phones when only LTE mode is on, user can't make and receive voice call.  On some phones user can't send sms after change settings. If you have above bugs and restart phone don't help try set preferred network to first at the top of the list or |Global auto|, |WCDMA| or other network which support sms and voice call in your country.