Idea Cellular Ltd — changed my SMS plan without notifying me.

I am an customer of Idea having my mobile number [protected] since last 8 years. In the month of march 2009 the company changed my SMS pack without telling me. I was having the scheme of 1500 msgs in 75/-Rs since last 4-5 years. When i received the bill and called the customer care they just said that they had sent a letter of intimation about the change in the SMS packs on 25th March 2009 containing the details and the migration process in case of no revert. We understand that based on the letter of intimation, you have chosen to accept the migration of the existing sms pack.

I have not received the letter of intimation till date. Everytime we want to make any change in plan then we have to call customer care and confirm about the change then how can they just change without asking me.
To clear this i called their customer care then the lady who answered the call was in such a hurry that without giving proper information she just wanted to hung up. I have mailed it also this to customer care but of no use.