Why is my data disappearing and why are u so expensive?

I started to realise that my data depletes like crazy fast. I have uncapped internet at my office so dont use my phone data much anymore. I checked to see if there is any programs running in the background but I barely use any. What happend to my data why? You are already the most expensive network so why on earth are you depleting my data so fast? On facebook there are hundreds of people complaining about the same thing so clearly there is something wrong. I am paying for this data when am I receiving my lost data back???