@Cassie1703: It should still be possible to make and receive calls in the absence of the VoLTE feature, provided that there are no signal issues in your current location. To troubleshoot the situation, head to Settings > Connections > Mobile networks > Access point names, and check to make sure that your network plan is registered here. If it isn't, tap the 3 dots in the top right > Reset to default, to see if this helps. Tap the Back button > Network operators > Select automatically, and make sure that this is toggled on.
If the problem persists, power off your phone, remove the SIM card and give the gold contacts a rub with a dry, microfibre cloth, then re-insert it and power the device back on. When the phone has finished booting, check the top left corner of the lock screen, where your network details should be visible.
If you continue to see the 'no network connection' notification, then please try your SIM card in another compatible phone, as this will help to determine if the problem lies with the phone, or your SIM/network provider.
