So today I called them up for downgrading plan, and initially they offered 799 plan as the lowest. I asked for disconnection and he told me 599 plan is available and again checked and finally offered 499 plan with Rs 100 discount.
Now it comes down to around 490 per month including taxes for 8 Mbps up to 30 GB + 1000 GB bonus data.
Eagerly waiting for Jio Fiber to launch now.