@ aragon4reaz…..i had a similar experience and had to place a call to their call center where I was briefed on the Android bundle plan.
Apparently the burn rate differs at particular times with the highest being 1.5kobo/kb between 10pm – 6am.This could be a reason why you think you are being ripped off.
Like fatnaija pointed out , if you have series of application running at the back ground i.e. Antivirus etc. this can also consume data without your knowledge.
I use an Android device and from the DATA USAGE section, you can actually see volume of data consumed within a particular time frame and apps responsible for this.