My Xiaomi Unicom card suddenly can't answer the phone, can't make a phone call, but can surf the Internet and receive short messages. What happened?

Suddenly I can't answer the phone, but I can send short messages online:

[1] Check whether the mobile phone is in arrears, and suggest to pay for recharging;

[2] Check whether the mobile phone is set with call forwarding, flight mode on and call barring. Suggest canceling and try again;

[3] Check whether the function or signal of the mobile phone is normal, and suggest to change the mobile phone or try again;

[4] If roaming to other places can't be used, it is recommended to check whether the local network signal is normal and whether roaming permission is enabled for this number;

[5] Try to restart or change the phone to see if you can answer the phone;

[6] Take the mobile phone card to the local business hall for testing or replacement.