Hi @gyaanpudasai,
That doesn't seem very good does it.
If you're getting an "unable to activate" error, Apple says it's due to their servers being crowded or some garbage.
I think referring to this video is better (I'll add a link but i don't know how this platform runs with links so hopefully it stays).
Basically, there's a chance (Admittedly, very low) that someone took your serial number, cloned it to another device and activation locked it. Now, the video doesn't quite show the same error as yours so maybe it's not applicable but it's worth a watch:
[link|https://www.youtube.com/watch?v=ifOifNBgyRg|https://www.youtube.com/watch?v=ifOifNBgyRg]
However, depending on the country, your device could also be blacklisted if you did something to upset the big providers for data. Again, this is far beyond my scope but is a possibility.
Ignoring both of those then, can i just ask a few questions (as the people here have already done so thanks :)):
1) Did you turn your phone on to suddenly see it locked or did you try reset it?
2) Is this your device from purchase or a second hand one
3) Are you aware if your provider has blacklisted you for any reason?
4) Do you have any outstanding transactions with your previous provider? This can affect your ability to connect your phone to internet but maybe not activation, but still a possibility
5) Are you aware of any restrictions surrounding apple devices in your country (Don't have to mention which country if you don't wish to)
6) Finally, is the activation lock linked to someone else's account or yours? Check that since that is probably the most important thing to consider.
Hope this helps, and I am hoping we can get your phone back to working order as soon as possible.
All the best,
Nick