Arduino Mega 2560 timer interrupts

Hi,
I'm trying to control two stepper motors using Arduino Mega 2560 and A4988s. Since A4988s require a pulse to operate, I decided to use timer interrupts. I'm using timer 4 and 5(There is no special reason to select those, please let me know if those are inappropriate). I'm new to micro-controllers and have some basic idea about timers. I wrote following simple code based on my current knowledge and it does not work as I expected. I have added 2 LEDs(I use LEDs to verify before using Motors) to pin 36 and 37, and those LEDs blink at same speed. But one LED should blink faster than the other LED. Please guide me to fix this issue. Thanks.

void setup() {
    DDRC |= B00000011;
    
    cli();
    OCR4A = 15624;
    OCR5A = 7812;
    
    //TCCR4A = _BV(WGM42);
    TCCR4B = _BV(WGM42) | _BV(CS40) | _BV(CS42);
    //TCCR5A = _BV(WGM52);
    TCCR5B = _BV(WGM52) | _BV(CS50) | _BV(CS52);
    
    TIMSK4 |= (1 << OCIE4A);
    TIMSK5 |= (1 << OCIE5A);
    
    sei();
}

void loop() {
}

ISR(TIMER4_COMPA_vect)
{
    PORTC ^= B00000001;
}

ISR(TIMER5_COMPA_vect)
{
    PORTC ^= B00000010;
}