Airtel — Data Balance deduction

Address:

Mumbai City, Maharashtra

Respected Sir/Madam, I have activated 3G 1gb data plan from online best offer on 1st sep 2015 on my mobile num-[protected] and as per the offer I got double benefits so I got 1.8gb data as per the offer.Yesterday I checked my data balance and it was showing 1300mb pending after that I put data connection off and now without any usage my balance is showing only 300mb. I am not using any Google app and you tube even I am not downloading any video or image on what's app also I have checked in my handset data usage its showing 719mb used only from 1sep to till date.so kindly help with my remaining 800mb data. As I am facing problem first time form airtel otherwise service is good even I visited in store also for the same but they told me that they can't do anything. so help me.