Fraud Sales

I have done internet recharge from the Airtel Recharge application of android phone, where they gave me the special offer of 1 GB 3G internet for 25 days on recharge of 179 rs. So I did the same recharge on 9.5.2016 and I got the msg of 500 Mb received in my account. After few days when I didnt got the balance Mb in my account I called up the customer care and they informed me that once the 500 mb is been used you would get another 500Mb. So my 500mb data ended on 23.05.2016. When I confronted customer care again that I havent got the remaining 500mb they are keep saying a single word and that is there system shows that they have provided 1 gb and they cannot do anything in it now. And as a part of solution they are asking me to wait it the cycle is over and than I can ask for the detailed bill which would show my gb usage.