Siti Broadband — nat type issue

Address:

Netaji Subash Road, Nadia, West Bengal, 741302

They said i have to pay 2300rs per year for open my nat type. But no other internet providers do the same. They did not close the nat type. But in case of siri broadband they fixed a price for open the nat type. This is simply wrong. Because when i use a vpn the nat type become modarate. I was like what a idea of siri broadband to steal the money of consumer. They need to remove the price & let the nat type open or modarate