Why a Samsung J3 wont call/text but data works

A friend and I own the Samsung J3 model phone. Both phones shared this exact problem within a day or two. The issue was the phone could not call or text. Neither incoming nor outgoing attempts were successful. The kicker was the internet still worked without WiFi. Any outgoing call failed saying there wasn't service. The problem was resolved by manually switching a setting in 'mobile networks'. Taking it off the network and putting it back on after a few minutes. I'm wondering why this would happen to both phones in short time, and why changing that setting solved it. Maybe the phone had an update that causes a glitch in that area? Any ideas are welcomed. Edit: wanted to also add the LTE data was on and operating with no Wi-Fi being used.