Airtel — my number has been allocated to someone else {fraud}

Address:

Vellore, Tamil Nadu, 632014

I was using airtel number [protected] from past 3 years. And on 9th august my number has been allocated to someone else.
All my credentials of banks, ewallets and otps from different online portals come on this number. I recently came across issue that someone else is trying logining in accounts registered with this number.
I have made a phone call from this number on 12th july and have proper proof for it, just to support that number was active in 90days period from now!
I wasn't inform inprior that services will be discontinued, niether on airtel number nor anywhere else.
Just a simple question, airtel can send thousands of mails on registered email address and can make hundreds of phone calls on alternative number, why can't they use this alternative contact information to tell something this important???
I am a trader and have to travel around the world. I simply can't afford to change the number.
Service call executive manikandan d and s. Murthy gives absurd answers.
If not solved with web complaints, i'll move to court of law with charges on airtel and new user of number, of seeking personal benefits.