Airtel
Wrong information given by airtel's

I have airtel's corporate account.i called up customer care service and asked for the ISD rates to call london.he told me Rs 6.40/minute. so i activated ISD on my phone.but when my bill came.it came with the charges of Rs9.20/minute.i again called at customer care and asked for same thing.he told me that its Rs 8.00/minute.agin i called up customer care and asked for the same.first he told me its Rs 9.20 and then told me its 6.40.

so i don't know exactly what are the charges? and i have to pay so high bill amount because of a wrong information provided by customer care executive of airtel.