I don't mean to defend any operator here. I used to suffer the same fate. However there are a few steps that could help one get the best out of the data package you use. I am sharing with you a few of these:
1. Get a data bundle.
Pay as-you-go internet comes with higher cost. Some network operators charge as much are 20 pesewas per MB of data as against less than 2 pesewas for 1 MB in some cases for a bundle. I never bothered about buying a data bundle when i was using my Sony Ericsson W810i. Once you are on android (for that matter any other smartphone), you may want to consider a bundle. It helps make some savings in the long run. The process is different depending on your mobile network.
2. Turn off Auto-Sync
The auto sync feature allows the phone to constantly monitor and update various apps that may be out of date. Background applications also rely on this feature a lot.
-Go to Settings > Wireless & Networks > Data Usage >Auto-sync
Make sure it is unchecked.This is also slightly different depending on which version of android you are using. If you are on 4.4 KitKat it is simply Settings>Accounts >Auto-sync.
3. Disable Auto Update of apps.
Apps are set to auto update by default. Open the Play Store >My Apps. Select an App, press menu, uncheck Auto-update. You can also disable auto-update in Settings.
You can as well avoid installing "unnecessary" third party apps. Even those that claim to check data usage end up consuming so much data in the long run.
Please note however that most apps still use data in the background even with all these measures in place.