it should be single IC for every led not single ic for each led
What's the difference? "Each" and "every" mean the same thing. How many ICs do you want to use for 20 LEDs?
If you want to use 20 ICs for 20 LEDs, you can get ws2811 chips.
If you want to have as few as possible ICs for 20 LEDs, there is tlc5940.
But by far the easiest and best solution would be to return or re-sell your LEDs and buy ws2812b LEDs.