How to remedy after the flow exceeds?

With the popularity of smart phones, many people will pack a fixed traffic every month, but whether it is 300M/500M/ 1G/2G per month, some people have already exceeded the traffic before the end of the month. And the excess flow is often expensive. I have seen many people with overloaded mobile phones, from young people to the elderly, from tens of dollars to hundreds of dollars. If you don't pay attention to these expenses every month, you will be deducted into the phone bill. Let's explain to you how to remedy after the traffic exceeds.