Oh no, fenghuicheng! I don't like the sound of this at all. We absolutely want to make sure your billing is accurate.
In this Community, we're not able to take a peek at your bill to figure out what we're missing - I know that typically four lines of T-Mobile ONE with AutoPay is $160 a month, so if your bills are supposed to be lower I'm guessing that's due to a promotion your account should be enrolled in? If the credits aren't showing up to reduce your bill to the correct amount, we definitely want you to Contact Us so that we can verify your account details and figure out what's missing here. If you'd like to try an online format, you're welcome to reach out to our T-Force team via Twitter (@tmobilehelp) or Facebook - our teams through those channels do have methods to securely verify your account details and hopefully get to the bottom of this so that you don't have to make these calls!