Airtel — airtel is charging on postpaid bill - (543212 not used or subscribed)

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No. Yediyur PO Road, 7th Block Jayangar, Bangaluru, Bangalore, Karnataka, 560070

Airtel — airtel is charging on postpaid bill 543212 not used or subscribed
Airtel mob no. [protected] being used by my dad who is 80 yrs, he is on a postpaid tariff plan of rs. 399.
My dad hardly makes 10 outgoing calls in a month, he is on a plan of rs. 399 supposed to be the lowest tariff plan, i had requested for a 199 plan few times, but i was told this is the least tariff plan, so except for receiving calls and making around max of 10 calls in a month he does not know or use any other service not even messaging service. For this i have been paying monthly around rs. 500 - 600 which itself is too much of an amount for the number of calls made.
But this month airtel has charged an additional rs. 360 for using the services of 543212 (The service of which was never used or subscribed by my dad). So after adding the above rs. 360 (Suspicious) charges and other call charges this month's total payable bill amount is rs. 1036.
Shocked on seeing the bill amount, i called airtel customer support 121 seeking clarification for rs. 360/-. The customer support executive told me, that the charges were for a voice call which was made to a helpline number 543212 for 1 hour, i told the executive it was not possible that it could have been used for 1 hr as my dad cannot hear properly and does not have patience to hold and talk on phone for 1 hr. After repeatedly trying to explain that it was not at all possible that the service was used or a call to that number made the executive bluntly said the amount was charged as it was used and hence the bill total of rs. 1036 must be paid on time, to avoid another rs. 100 late payment fee etc.
This is a serious issue, we have been loyal airtel customers for over a decade now still, it is so disappointing to be charged for something that was never used and is not at all acceptable.
I request through this letter, to consumer complaint forum that this issue be looked into and resolved in order for us to continue using the services of airtel and we be charged only for the services used and not otherwise. Any other details required to prove the case will provided if required.
Regards,
Vijaya
[protected]@gmail.com