Airtel — airtel mobile - postpaid unauthorised payment deduction

This is to inform that an amount of rs.15099.28 in the month of jan 27, 2020 towards international roaming charges. I have not authorised this payment and not activated any international facility. I have written and also spoke to the customer care service of airtel many times for refund. First they have mentioned that they can refund some thing around 5000/- verbally during my telephonic conversation later when i asked for the confirmation there was no response. Till april i have been expecting and continuously following up with them but without any response. Later i have deactivated the airtel app in my phone and deactivated the si for the credit card. But to my surprise they have deducted an amount rs.790 on 27th march 20.
I request you to nkindly investigate and get refund of the entire amount