Airtel — overcharging on international bill

I am currently residing in Egypt. But have kept my Indian number active as I receive all my bank OTPs on it. I have subscribed to a RS.3999 unlimited plan for incoming and outgoing calls. Yet, Airtel has charged me rs.649/day for an unlimited incoming pack. Making the bill a grand total of RS.18, 018. I don't even use mobile data on this number. This is a ridiculous amount and I would like Airtel to resolve this dispute immediately. Since I am residing outside of India, I am unable to contact them on the 121 customer care helpline.