I turned my clock off manual to automatic and it worked.. worth a try
Hello. Having an issue where my phone is not allowing me to make a call.
2 replies
https://9to5mac.com/2017/11/15/att-outage-fix-iphone-calls/?pushup=1
You would probably need to turn your clock to manual and then back to automatic. The two suggestions from AT&T are easier.
Phone not calling