Airtel — unwanted charge for my airtel number

Address:

Cooch Behar, West Bengal, 736135

My number is [protected].
It is an airtel number and airtel is deducting rs 20 every now and then and i am not being able to stop this service for once and for all. Please help.
I have called them many times but they have not helped me to resolved this.in general i don't use any value added services but yet i am being charged and i want refund for the rs 20 and i want this harassment to stop.
I do not require any value added service. I never opted for it. They have automatically did something and deducted the amount and continuously deducting my hard earned money. Please help me to put a stop on it.