Vodafone – Company not providing information about services completely and over charging later

Location/place: Bangalore

Name of company/service: Vodafone

Hi!

I activated my Vodafone 2G Internet plan as per which 2GB of Internet is free for a payment of Rs.99 everymonth. I am a postpaid customer.
Normally my bill is approx Rs.400 . Recently i received a bill of Rs.1746.
When i had a look at the bill, i see that they have charged me for the Internet usage while i was in roaming.
When i enquired , the Vodafone Customer support told me that i am charged because i used Internet on a different carrier.

I feel cheated because i was not informed of the same while activating the 2G Internet Plan. Had they informed me before hand of the same, i would have not used the Internet Plan and my bill would not be so high.
This is clearly a case of not providing complete Information to the Customer by which they can overcharge the customer.
Please help.

Thanks,
Randeep