My dear reset network setting both Sim and then reset all setting of your's device in general management setting. Also complaint to your's service provider telecom company on their customer care for Volte not showing/ working. If you like please accept as a solution. Thanks.
Please perform the below mentioned steps to resolve the issue:
* Check network operator settings Settings > Connections > Mobile networks > Network operators > Select automatically > OK > Registered on network.
Note: We recommend to set device network operators as LTE/3G/2G (auto connect) mode.
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
