First Install Prepaid Manager. Installing will not let you to use these app. You have also install a configuration file in which all settings are there called serviceproviders.xml
sudo apt-get install libxml2-utils
if faile use command su instead of sudo.
open file manager in admin mode
or sudo namo .....
and search for serviceproviders.xml open in text editor
look for your service provider.
where to search this file
First Look for your operator like Aircel, Vodafone, Relaince .....
and add before <apn></apn> tag
Save the file and use Prepaid manager software.