Airtel — my number given to another customer

I used Airtel number 99441***** more than 8 years.
I traveled to abroad and not able use 3 month. Try to use on 26/07/2019 and it's de-activated..send mail to customer care on 26/07/2019 and they replyed It's de-activated 8/06/2019.and asked my details to activate. But 30/07/2019 it's activated to new customer.
I called customer care and they 90 days inactive so we given to new customer.

I am not understand .how they can give existing customers number to new customer.

I need my number. But airlel not giving which I used 8 years.