Airtel — overcharging international roaming

Good morning

I am a loyal airtel customer from last 2 years having postpaid no [protected]. Currently i am on a visit to austria and i activated an international roaming (Rs 149/-) without any specific plan on 1st january 2018. My credit limit is 3600, however despite not making or receiving any call i was charged a bill of rs. 5106/- for 6 days.
1. How you made a bill of 5106 when my credit limit is 3600/-
2. If you activated a plan of 649/day on my number why i was not notified of the same.
3. Even if you consider 649 for all 6 days still it doesn't match with final figures.

I want you to kindly look into the matter and respond.
I wont hesitate in approaching consumer forum for the same and switch to some other operator as soon as i reach back.