Focus on getting real Cashback at the time of using the card. And, take advantage of auto bill payment options given by almost all banks. Even if there is no cash incentive in paying bills.
Primary aim should be timely payment and ABSOLUTELY NO HEADACHE.
Avoid such unregulated n dubious 3rd party Apps/websites. The resultant headache is NOT worth taking the risk for 1% to 3% benefit. Our time, our hard earned 100% money n effort is much more valuable.
We got better things to do than pickup a fight with such fraudulent firms/Apps/websites.