if you dont like what ATC says ignore it and press on restating your intensions.
The decision not to grant landing clearance is not in ATC's hands. This is very much a political thing. Should you choose this course of action it is entirely possible that all the runways are blocked by ground equipment. It has happened before.
BTW It isn't mentioned anywhere in the article that New Delhi was actually the closest airfield, just the most suitable; commercial interests at work here? Also, what was the difference in flying time between Going to New Delhi or to Kolkota?