Why did China Mobile wait for the traffic to run out of 800MB before sending a message to remind me, when I received the message, the traffic had exceeded 800MB?

Hello, I have eaten this before. You need to check the traffic information in time, and then you turn off your mobile phone. This is the first time you said that you can call him, just like I did before. Will he give you a refund? You said, why didn't you tell me there was traffic, didn't tell me in advance, and my money was gone, and then he would let you turn it off every time the phone was running out, so you said you knew, and it would be more accurate next time. ! !