This is something I discover by chance when I have 700mb of data and 3 days to month end. For your information, my telco will charge me $10.70 per gb that I exceed for my mobile data usage.
However, the spike in my data usage is mostly linked to underlying apps running & videos on Facebook.
My solution is to turn off my mobile data! It works so well that I enjoy privacy time as my messages on Facebook and Whatsapp only come in when I have wifi.
I had inform my loved ones to call me if its urgent & use the tried and tested "sms" to reach me. All is good! Of course, turn on m0bile data if its urgent. Enjoy!