Tata Docomo — sim card invalid

I got transferred to different location but i was using the same tata docomo number. I had to use another sim for 4 - 5 months. But when i switched back to my docomo number it is showing incorrect number, invalid number and whenever trying to call it is showing not registered on network. The reactivation of the sim is very important for me. Kindly help me on the same. I will be really grateful for that.