Tata Docomo — sim service stopped working

Address:

Pune, Maharashtra, 411019

I have been using the tata docomo sim for more than 2 years, one month ago the service stopped without any notice.
When i called the customer care they said that the number has already ported to some other carrier.
I recently got to know that the airtel company has baught tata docomo network and docomo service providers were requesting customers to switch to airtel network from phone settings.
I did not receive such call or message, the service of my sim was stopped without any notice!
Please do the needful