Honestly speaking, no brand will provide you support for a device which is purchased from another country. The only exception being a few products which come with an international warranty.
Also, the X5 is a device exclusive to China. The software is unique, as per the requirements of the country and, the global support knows nothing about these phones. So, I think their replies are justified for a device which is not launched in India and when it does, it will run a different software. That said, Nokia support barely gives proper responses to even devices which are already launched, so that needs a big improvement.
And to my understanding, only Jio's VoLTE will work on the Nokia X5 in India. The other operators such as Idea/Airtel shall not provision VoLTE on the device. Do let me know if it is different in your case.