Bharti Airtel - False Billing

This is regarding harassment i am facing due to Bharti Airtel, for my cell phone number ********** & other family number , for charging me wrongly.
I am travelling abroad since **th Jan ****, before leaving i requested for deactivation of Internet data while travelling and it was done by very competent Customer care representative, till **nd July ****(Returned to India), i was not charged even single penny for any Internet usage. everything was as applicable. This representative educated me of all these international charges and how to avoid them. Again when i was about to commence travel abroad, this time on **rd July, before that i made the same request to Airtel customer care and I was assured by this Customer care rep that it will not have active Internet data during international travel, I was confident.
And i got more confident because when i reached Nigeria airport my internet was not working.
In month of Aug ****, i experienced that I was unable to receive even OTP , my wife complained to Airtel and their representative did some Technical settings, we told clearly as i am abroad, i don't want internet but SMS should come. SMS issue was fixed.
Surprisingly when we observed our September bill, it was showing international roaming internet usage, we again complained, it was communicated that its corrected. and then also they are charging abruptly for service i am not using.
Above all, this phone is just to receive OTP sms, nothing more than that when i am travelling, so there is no point of using any internet on this phone.