Idea Cellular Ltd — Scheme purported "free" actually had hidden costs (Post Paid User)

Address:

Pune, Maharashtra

Idea Cellular has been popularising discount scheme called " Double talk time" for Post Paid users.
There was a call on 11th of Sept saying "Your number has been selected as preferred user and we are giving a discount of Rs. 75/- for next one year" When asked for charges, it was clearly stated that there are no charges whatsoever on this scheme. So I activated the scheme.
But to my shock Idea deducted Rs 750/- for this scheme in the next month's Bill.
I enquired through mail to which no response was given.