Airtel — activation of prime zone automatically

My balance got deducted unknowingly and later I found out this message "Thanks for using PrimeZone. You have been charged Rs 20.0 from your Airtel Mobile account.For more services, call 56789". So on 09/09/2018 ₹20 got deducted in my main balance without my knowledge. I want Airtel to refund my money as I didn't activate the service.