My iPhone X is not ringing, it shows missed call
Hi, I have an issue with my iPhone X: the phone is not ringing, it is shows a missed call for about 50% of the calls. When some people try to call me, the 1st time it goes straight to voice mailbox or hangs up. Usually when they call me a 2nd time it rings. Apple Care sent me the steps“If you can't make or receive calls on your iPhone” to be followed and I did all but still the same. Anyone had this issue? How to fix it? Thank you for your help.
iPhone X, iOS 11.4.1