If 16 Mbps is feasible in your area, then you don't have to pay any extra money for 16 Mbps. New tariff plans are not based on speed but Data limit.
Call Nodal Office/Appellate authority to ask for explanation why CC is asking for 200 Rs additional to upgrade your speed from 8 Mbps to 16 Mbps. 1399 Plan should give you 16 Mbps/25 GB if 16 Mbps is feasible in your area. Its as simple as that.
CC told me i would get 16 Mbps on 1399 plan when i asked them last month. But i am on much better retention plan so i didn't take normal 1399 plan.