Hi,
just wondering if this might be applicable to you. "You need a 4G/LTE plan to use your operator's 4G/LTE network for voice calls and data services.
Check with your operator for details' Have you selected 4g/lte ? I'm not certain where it is in your phone check settings > wireless & networks > more > mobile networks > network mode. If so try 3g and see if it works. Some carriers do not have voice service on 4g/lte network. i