Airtel — purchase 6 months both data & voice but airtel is charging monthly.

Address:	Hyderabad, Andhra Pradesh, 500050
Website:	Airtel

When I interacted with Airtel customer care executive, he has explained 6 month plan for voice and data. But, Airtel is cheating me by charging monthly for what purpose God knows. Executive told once in six months, so paid once, now they are generate bill every month. I don't understand why they have 6 months plan and again monthly bill. I have call recordings. I don't expect Airtel to stoop down to this level and swindling money from customers in a broad daylight.