Recharge Rs. 100 four times with different sites to get maximum cashback & Activate Rs. 399 pack
If You Still want direct recharge then go for My Jio App
Certain operators provide the option to activate plan from "Account Main Balance", So when you are recharging Rs 100 for four times, it is not for activating the plan, but just to add to your Main Balance. Once you have enough in your Main Balance, you can activate Rs 399 plan and opt to "Pay by Main Account Balance". Thus you get the plan you wanted, and while doing the individual four Rs 100 loads, you can avail offers from multiple sources.
Be sure to check first that the operator allows Pay via Balance for the plan you intend to activate eventually.