From Setting> General Management > Reset> Reset network settings
FYI: This will uninstall your Bluetooth devices and you will need to re-install them
I understand how frustrating this is. Here are some troubleshooting steps you can try to get the phone working again for those calls. https://www.samsung.com/us/support/troubleshooting/TSG01001613/
You can also try checking your APN settings , reset those to default ** make sure you highlight the apn button on the left after resetting**
Settings-Connections- mobile network -APN - reset to default
If the troubleshooting is not helpful, you will need to follow up with your service provider for additional troubleshooting steps.
In the event the carrier is unable to assist, it is recommended to have the phone evaluated by an authorized service center. You can use the following link to find a list of service centers in the U.S. that can do the repair: http://www.samsung.com/us/support/service/location or by calling customer support at 1-800-726-7864.
For assistance outside the U.S., please use this link: https://www.samsung.com/us/common/visitlocationsite.html
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