I used Tata Docomo network before 2 years. Because of their poor service, I ported my number to Airtel.
Their network is very poor and we wont get signal in many areas. Often my friends told me they tried to call me and I was not reachable.
Even when I tried to make a call, sometimes it wont connect on the first attempt. I have to make repeated attempts.
Their customer service is also not that good and they will put us on hold often.
Nowadays all other networks have also slashed their charges. So there is no difference between Docomo and other network’s billing.
My humble opinion is, it is better to port to other networks.