Airtel — activation of games subscription without permission

Address: Kolkata, West Bengal

Dear sir,
My grandmother has been charged ₹120.00 on 11.12.2017 on her airtel number with an sms saying "thanks for choosing adofgames...", while no permission was asked prior to that and since she is 76 years old, so she is incapable of reading sms-s let alone confirming offers.
When the customer care was called and asked for refund, the service provider mr. Bikash adhikary said that the subscription was confirmed by sms confirmation on 4th december (No sms came on that day) and would again charge the same amount next month if not stopped. Neither did he refund the money, nor did he treat us with respect and kept on using sarcasm as defense. This is unacceptable and now the phone balance is ₹0.49 with which no calls can be made in case of emergency. We are afraid to recharge the phone as the same may recur again. This is not the first time airtel has deducted money in such unjustified manner, but in the past i did receive refunds in few occasions after much harrasment. I wish this money be refunded too. Kindly guide who else to complain.