Q: Why does my iPhone 6S while using Cellular Data is consuming to fast the balance?

I recharged my balance on my phone and when I turn on the Cellular Data, it just consumes it to fast; even if there is only few apps enable to use Cellular Data.

And also I have only use 40Mb in internet data in my phone, since it is a new iPhone. One more thing, the first time that I have recharged my balance, it only last one or two days. Here I have friends that also have, well only iPhone 6, and in their phones the same about of balances that I recharge, for them that amount lasts like more or less a month.