I was with Tata Docomo for 10 years. I don’t know why I stayed so long.
The connection was often extremely slow or completely down for long periods of time, like days. It always took a long time for them to send someone, or get their server back up, or resolve whatever was the problem.
Customer service was usually not helpful, just reading from their script, keeping you on hold for a long time, couldn’t answer questions satisfactorily. They always promised the connection will be back "in a few hours" or "tomorrow morning" and it was never true. It was like talking to robots. They drove me nuts.
Once the society where we were staying had taken the cable down, so the connection was gone. Tata knew this but kept me hanging for days with false promises, and never told me that they had to get permission first to put the cable back. All in all it took 2 weeks, and they kept lying to me on the phone, keeping me in the dark. Terrible.
Then, another issue was that sometimes my payment for some reason did not arrive in their payment accounts, although I had paid in cash before the due date. They did not inform me that they had not received the money but simply cut my connection. Even when I told them on the phone that I have the receipt in my hand which has the date when I paid they refused to re-connect me. They said they had to "check" first. It took them days. On top of that they wanted me to pay a "late fee", even though I never paid late - not once in 10 years had I paid late! They were not ready to trust me as a long standing customer. This happened several times, and that was the reason I finally in 2015 changed to BSNL.
I can not recommend them. How they treat customers is disrespectful and simply wrong.