Why can't I call or text and still use internet?

i had the same problem so i went to settings >connections>mobile networks and switched it from LTE/3G/2G to only 3G/2G and it worked now i can make and receive phone calls

First I would update your phone's software. For my Samsung Galaxy S21 FE I've been having my phone say "Searching for service" on the lock screen and it will say not registered on a network when trying to make a call. No calls or texts but data works fine. What worked for me was going to Connections > Mobile networks > Network operators, unchecking select automatically and selecting home. I think it is a software bug with my phone that causes this because it seems to happen randomly and will resolve on it's own after a day or so otherwise.

Mine did the same thing no text or talls but just fine internet not wifi in a friends home who had the same carrier but no issues? I figured out changing network LGE/4g/3g to a lesser communication network or switching it up was only way to get or receive calls and texts but was still unable to figure out why nor could i figure one network that stayed working in her home just for some reason, no one could answer after many calls and trips to my carriers store, i had to keep switchin up my network conection to use my phone in this home or even close to it , i began to think she had something in her home that caused the issuse , a scrambler or phone blocker that a tweeker may use tripping about phones in their home , i nor anyone on my carriers troubleshot line or in the store never could figure out just what it was

I tried all the answers before me, but it still didn't work. Then I try on/off airplane mode for several times. now it works at least for me. maybe worth to try

I just restarted my phone and it worked. Same situation. Calls would not go through and would hang up any incoming calls. Facebook messenger worked for calls and internet had no issues. Just a quick restart and no problem.