best way to pay 25k cc bill for reward ?

Use supercoin 

I do not know how to use supercoin for bill payment 

FULLPAY on Mobikwik works wonderfully well for 1% cashback upto Rs 50 especially after all CCs went live on BBPS platform. Earlier you would need to give access to your email / SMS but now there is no such need.
Mobikwik also lets you use 100% of your Zillion (formerly Payback) coins at 4 coins = Rs 1 ratio.
For the first CC payment of the month of Rs 10k or more, it lets you use the 250CASH coupon for typically single digit cashback.
Lastly, Mobikwik also lets you use 15 Supercash on minimum CC bill payment of Rs 5000.

I can't believe I said 4 positive things about Mobikwik at one go!
I am pretty sure Mobikwik is going to block some of these avenues soon or narrow them down.

imo, sbi unipay is best as it gives 1% of hdfc DC.

yes