1G gone in 2weeks from whatzapp only

ok I got issues with my data am ok with certain billing even unfair once to a certain point cz am always complaining. now I get 2G on the 19th September 2017 and today on 03th October 2017 am on 20MB. what confuses me is how is that humanly possible when I only use whatzapp as am not on any social media feds? they tell me to check my settings and with using phones for this long will I honestly not know how to switch off background data and automatic updates? come on. I disabled all other apps even emails but data is just flying. I need a real explanation and if they can not show me a graph but show me like a paper showing whats been eating my data and how. I switch my data on and off when I reply but still. am never online because I work and I use my work pc for any google stuff.

I need to know if they failing me and I can just change networks and please reimburse me because I bought that data. it wasn't given.

Regards upset client