unauthorised deduction of rs.30

I mistakenly clicked an ad on an app in my android phone n before i knew it, Rs.30 had been deducted from my airtel account balance. I haven't talked to thr customer service center as yet since i never get my query resolved and am always left fuming everytime i call the customer service center. I would like the balance to be reinstated in my account. Kindly tell me what i need to do for the same.