Airtel — charged rs86 from my prepaid balance

My phone no. Is [protected] (Delhi ncr). I was charged rs86 from my prepaid balance without any prior approval. It was done on 14th april 2018, the message was -
Voice - rc86-local/std calls at 30p/min - 28days has been renewed on your airtel money. Rs 86 has been charged to your account.

I didn't ask for any automatic renewal. I also checked the value-added services in my account and there no such service i opted for.

Kindly refund my money as soon as possible as it was charged