For whatever reason, this line below may be missing from /system/csc/feature.xml
Copy/Paste to feature.xml as the last Common entry in row-line-format with a root browser if it's not already there. Save and reboot. You should see Wi-Fi Calling back in Settings if that was the issue.
Sent from my SM-N910P using Tapatalk
Thank you that worked for me as well.
Sent from my SM-P900 using XDA Premium 4 mobile app