It is better to control your Apps from running in the background.
Have you check for virus &or malware, that may cause the background running, although you are unable to see which apps (hidden).
There are a lot of free anti-virus available in Google Play.
When you activate the apps, and then close the apps, but that apps will still continue in the background.
You need to check in the "Recents".
Depend on the phone model, mostly have to press + hold the Home buttons.
Then Removed those apps stated out of the Recent tray.
Next is the mobile Data running in the background.
If you know you are within wifi range, then disable the Data.
When you are outside and not using internet connection, then disable the Data.
This will force any apps not to run in the background for connection.
As most phones do have many good features, then use those features,
Such as @CheeSa had mentioned, set the limit on data usage.
Happened to my iphone too. Seem to happen only recently. Something don't seem right.
Firstly, mobile data for 4G plans calculation is based on both Upload and Download.
The charges of mobile data is calculate by per 1GB block.
The rate is based on 0.0107cents/KB up to maximum $10.70/GB, capped at $168/month. (incl gst)
For the rate and info, click here.
A simple calculation: For 1MB = 1,000 KB x 0.0107cents/KB = $10.70 charges up to 1GB. If the user had used up to 3GB (let say based on 4G-3 with 3GB) then the mobile data free 3GB usage end here. Any mobile data use from 3GB the calculation remain the same. So if usage is 200MB, the charges will still be $10.70 as part of 1GB capped. But used is 1.01GB the charges will be $21.40 Calculation of frist 1GB is $10.70; plus the exceed 1GB which is the next 0.01GB is $10.70; Total $21.40 Even if excess usage is 1.5GB the charges of $21.40 remain as 0.5GB is still within the next 1GB charges.
As what @CheeSa had mentioned in his post, using the mobile to monitor your usage.
Mobile data charges is based on both Upload & Download.
This is not as what incoming call is free, and outgoing call is chargeable.
Someone did wrote here by saying s/he had only using mobile data to transfer 2GB data to another phone.
Hence s/he asked why it charges is 4GB, not 2GB.
The point is 2GB for upload plus + 2GB download = Total is 4GB.
This is the way i understand how mobile data charges apply.
I am not Starhub staff &or related to.
Error in calculation.
Do refer to this link for more info here
A simple calculation: For 1MB = 1,000 KB x 0.0107cents/KB = $10.70 charges up to 1GB.
this is so wrong...how can you suddenly inflate 0.0107cents to $10.70 doesnt 0.0107 cents mean 0.01 cent
which when multiplied by a factor of 1000 should still be 10 cents not 10 dollars. 1 cent times 1000 is 10 dollars here you are talking about .01 cents. right!!! or else starhub should write $0.0107/ KB which means 1 cent per KB which is then equivalent to 10 dollars for 1 MB.