A. First, ensure that your device has the latest software update installed. Go to Settings > General > Software Update and check for any available updates. If your software is up to date, check your cellular settings by going to Settings > Cellular > Cellular Data Options and ensure that Voice & Data is set to the correct option (usually 4G or LTE).
B. If calling issues persist, try toggling Airplane Mode on and off. This can refresh your connection to the network. Additionally, check if your device is set to the correct carrier settings by going to Settings > General > About. If an update is available, you will see a prompt to update your carrier settings.