Airtel — cheating with special offers messages

I was messaged repeatedly with an offer of 1gb/day and local/national calls free for a period of 84 days for rs.399. I believed and recharged. The notification sms that comes on recharge said some other plan (2gb /day for 28 days). I immediately called customer care and was told that i can ignore the message and the plan validity is for 84 days only. I believed and told my wife also to recharge with same amount. To my shock, on 28th day after recharge, calls and internet were charged. When i called customer care again, i was told that the plan validity is for 28 days and inconvenience is regretted. I wrote to the appellate authority and nodal officer who called me back saying that nothing can be done and my frustration is understood and regretted. How can they cheat customers like this? They didn't even realise that the mistake is on their side. This is so ridiculous.