Airtel — increase in postpaid mobile bill

I am an Airtel customer since 2012 and I switched from prepaid to postpaid in 2016, before moving abroad. From 2016 till 2019/July the international roaming bill and the basic plan bill remained same, however, since Aug/2019 the bill amount has been suddenly increased approximately three times the original amount. I have analyzed the bill and it says the charges are for internet usage, while i have not switched the mobile data services from July/2019. Furthermore, I have been trying to contact Airtel customer care for NRI's and there is no response from the company.