Update:
Called-up MTNL, the aunties there are confused and was blaming the system that if the plan is unlimited, then its should not show any type of limit (something which I dreamt of), to which I had to explain that you ppl put some sort of FUP (which is 150 GB) and is utilized. So pls gimme more. I even lost 50 Rs due to the data balance being used up and the remaining main balance started getting less.
After couple of phone calls + each time of clarification to them, they gave me 100000000KBs (~ 95 GB) along with the deducted amount from main balance (50 Rs).
I believe that the auto renewal of the data balance is not present (rather than their claim of not working) and the new quote given is clearly entered manually (unlike the person above who got total 150 GB more). In any case, will call them up again when this given quota is exausted