Oneplus one network issue

I purchased one in January and rooted to put Oxygen OS at the time of release. Everything was working fine until a week back I dropped the phone and the screen broke. I couldn't check the exact issue but since service centre people asked me literally 12k to fix it I contacted another know service person and got the screen fixed. From the time I got my phone the imei number is missing and I am not able to use my sim, when ever I insert my aim I get an error saying "error in searching for network". The sim works perfectly fine with other phones and on other oneplus one as well. To resolve this, I followed a post and re flashed my one plus one to stock again by fastboot. Now my phone recognizes its imei number but the network issue is still there. Once the network was registered and I was able to make couple of calla but that don't last more than a minute. I am not sure what to do at this point and any help would greatly be appreciated. I am from Bangalore, India and use Tata DoCoMo as my network.

Thanks!

Hemanth V