First, please check whether the mobile phone is set with call forwarding, flight mode, call barring, etc. I suggest you cancel and try again.
2. This number has been stopped, which affects the call. You can check the status of the number. If it is not normal, you need to restore the normal state of the number before you can answer the phone.
Please check whether the mobile phone is in arrears. If it has been recharged, you can check the recharge status.
4. Please check whether the mobile phone card is damaged or not inserted correctly. You can go to the local business hall to test or change your mobile phone card.
5. It is suggested that you can restart or switch flight mode and try again. If you still can't answer the phone normally, you can also change your mobile phone for testing.
If this is not the case, you can contact the local manual customer service for feedback.