How to deduct the cost of choosing a package in 28 yuan when handling a mobile card?

This package is like this. Your monthly basic sales volume is 28 yuan. 28 yuan money includes 50 minutes of talk time, 100M traffic and 150 short messages. Whether you use up the money within one month or not, you will be deducted from 28 yuan money and start the calculation again next month! If you exceed the package, you will be charged extra!