Thank you for your asking. Kindly provide the information below so that we can better assist you.
1. Did the issue appear at the first moment you bought the phone, or does the issue appear after any system/apps' download or update?
2. Insert your SIM port with no SIM card, then put the SIM back and re-insert again
3. Does the Wi-Fi and the bluetooth perform properly?
4. Please try SMMI test
Calculator> type ".12345+=">SMMI TEST>Single Test>SIM Card Test/SIM Signal Test/Wi-Fi Test
If any of the SMMI tests fails, kindly bring your device to the nearest ASUS repair center for device checking: https://www.asus.com/support/Service-Center-All-Countries/
If it is impossible to access the service center during Covid-19 period, please try Call us: https://www.asus.com/support/CallUs