Airtel — unlimited pack balance auto deduction

I am using airtel from a very long time and i really like the service but i started facing a problem from few months. I use unlimited packs so i recharge once in 3 months. By the time the pack's validity is getting expired i'm getting texts saying (Recharge before the end date or else 23rs will be deducted). I dint not like this.. Why will you deduct if i dont recharge. For more clarification i contacted customer care.. They gave me a code.. To stop auto deduction but that is not working.