I would have switched to alliance for sure if we had the service available in my locality.You can try contacting Siti customer care or LCO, after which any one of the following will happen:
70% chance: they won't understand what you're talking about
30% chance: they'll ask you to get a Static IP which costs extra and is not worth getting if the ISP is Siti.
How important is it for you to get a moderate/open NAT? Because you can try moving to other ISPs like Alliance.
A part of Dankuni has Alliance and others whereas the only operators in our locality are Siti and Meghbela.
Does alliance provide Open or Moderate NAT without any hassle?