Are you tethering your internet to a computer?
Back when I had Verizon, I hacked my Motorola Droid Razr Maxx (4.1.2) to have free mobile hotspot. I noticed the same thing: that Android OS was using a ton of data. However, the math didn't add up. I had 4gb of data, but when I'd get an overage warning, I'd look at all the numbers, and mobile hotspot and Android OS added up to way more than 4gb. I concluded it was just a glitch, since it was hacked, caused because the software just didn't know how to report it accurately.
For example, I'm currently using a 4.2.2 Samsung phone on T-Mobile (unlimited), and I've used a proverbial #@%$ ton of data doing USB tethering with PdaNet+, yet PdaNet+ doesn't show up as using data. My billing cycle resets on the 7th of each month, and loading up the T-Mobile app, it says I've used 262.66GB of data. On my phone however, it says that I've used 474GB. But Android OS only lists 68.65MB. With my Verizon phone, I used wi-fi tethering. On my T-Mobile phone I use USB tethering (and some Blu Tooth as well). So that could explain that discrepancy, or it could be the different Android versions.
Either way, OBVIOUSLY, something is wrong with the way Androids track data usage when it comes to tethering. If you tether, my advice to you would be to actually add up everything listed in the data usage, and then compare it to what your provider says you've used. I have no clue what it's like in India, but in the US, every major provider gives you an account app that, among other things like payments and plan changes, tracks your data/messaging/minutes usage. If tethering is the culprit, go by what your provider says, NOT by what your phone says.
If you don't tether, I don't know what the heck the problem could be.