Cheating Company

Hello, I'm not sure if I selected the right "law" for this. I was an airtel prepaid customer and received a communication that there's a lucrative postpaid CUG offer for the employees of the company I work officially. I wrote to the email provided in the communication and received a positive reply that the plan I requested is available and requested me to change my prepaid to postpaid. I did so, and while doing so, the Airtel Relationship Center serviceman said that they don't have the plan I requested and said perhaps if I write to the same email on which I got a positive reply, I will get the plan. Until then, I have to choose a different plan. Upon confirmation that this is possible, I choose a random plan they offered and after a successful verification and stuffs, I got my postpaid connection to the same number I used in prepaid. Now when I email to the same address in which I got the positive confirmation about the plan I requested, they said that the plan is out of market (within 3 days!). After I said I have proof of the offer, they said they cannot activate because of the plan I choose now. There's no feasibility, they say. Is it possible to take any legal action against Airtel for this?