My mobile phone number is empty, and someone asked me to pay the phone bill.

It is the phone bill owed by the user's previous mobile phone number.

For example, Unicom numbers are divided into prepaid and post-paid numbers:

1 Unicom prepaid number: it means that users need to pay to use it, but once there is no phone bill in the mobile phone number, they cannot use it. So if it's a prepaid card, just throw it away when not in use.

2 Unicom Postpaid Number: It means that users can use the card first and then pay. After opening the card, they can use it without paying the phone bill. Generally, the post-paid card allows the user to owe money for up to two months, and stops after two months without paying. Therefore, when users do not use this card, they need to handle the related business of stopping or canceling the number to avoid arrears.