Rent not paid by government department what can i do

Hi All, I have a commercial property in Chandigarh, rented out to a Punjab Government Vigilance Department. They have been delaying rent from the last couple of years and situation has even worsened now with almost 4 month rent pending from their end. Whenever I ask for a rent, they usually tell me that the bill has already been sent to Treasury department. But, the reality is Treasury doesn't have sufficient funds. That's why they keep on delaying rent. Could anybody please suggest what can be done in this matter?