Airtel — abnormally high bill without much usage

Address:

Daranga Assam, near Bhutan gate, 781360

Postpaid no - [protected]
Plan-499
I am in indian army posted in daranga assam pin-781360.
I stay near indo-bhutan border on the indian side.
I use a bsnl number and airtel number, but for no reason the airtel sim is catching bhutan network and all calls are going as international calls on the indian side of the border. But it is not with bsnl and my bsnl postpaid usage is more than airtel and still bill is 442, how come airtel has given me a bill of 11200. My average airtel bill is around 500 monthly. There is no reason someone staying on near the border should be charged international charges. Moreover my army camp is on the indian side of the border.
Kindly look into the matter at the earliest
Else i have to go to consumer court