Airtel — invalid coupon for recharge

Address:

Kolkata, West Bengal, 743503

Yesterday, I bought a new Airtel recharge coupon from the local market to do some important work. Today's morning I entered the coupon number as usual but it gave the message that coupon is invalid, so I complaint to the store from where I bought the coupon but they said that it's right coupon. I called to the Airtel customer care executive and they asked for the serial number of the coupon I told them they said the serial number of the coupon is invalid. I informed the store but they said to report at Airtel store, so I want to registered a complaint and please inquire about this and take action it's not a small amount of money but it represents the image of the company.