The other party's mobile phone has been stopped, and this state will occur without the phone bill.

The possibility that the phone can't get through is as follows: the mobile phone user turned off himself, so he can't get through. The location of the mobile phone user is not good, and the phone with good signal can't be received. There is also the other party's mobile phone number is busy, commonly known as busy tone. The rest is the phone itself. Restart the phone. Or there's another one who just opened do not disturb mode and can't answer the phone.