My Unicom card can send short messages online, why can't I make a phone call?

The common reasons why mobile phones can't answer calls and their solutions are as follows: [1] Check whether the mobile phone is in arrears and stop, and suggest paying; [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.