Airtel — wrongly Billed - with extra data usage

Address: Kolkata, West Bengal

I have 299 postpaid plan .I am supposed to get 720 MB 3G data free ..I used 703 MB till 16th april and then i stopped using internet as I was about to exceed limit.I also checked on 25th april.It showed 703 MB used.I got bill from airtel on 27th April, saying my data usage was 779 MB.I have proof in sms that my usage was 703 MB till 25th April and Bill also shows i used internet last on 16th April. Moreover My airtel number was activated on 4th April and they are charging me one month bill amount from 4th April to 25th April