I was able to track down his actual phone number and on Facebook. Messaged him and explained to him. He wouldn't act. He said he intentionally gave a random number since he didn't want to be bothered by their phone calls and asked me to "deal with it".
Finding no other option, I used Tata sky IVRS service calling from my mobile number(linked to his account) to subscribe to a bunch of expensive channels, totalling the monthly subscription fee to 10x of what his usual fee was.
He reached out to me requesting that he be allowed to take control of his account, as he is unable to change the phone number linked to the account, without an OTP (one time password) received on the existing number (which was my number).
Did take some sweet revenge by not responding to his request for a while, but eventually gave him the OTP after a week.