Flight got cancelled and i lost out on seat bookin

i booked a flight with kulula scheduled for 18:30, after confirmation of the booking and payment and i reserved 2 seats at R70 each. i get a call after informing me that the flight was cancelled and asked when would i like it to be moved. after some back and forth i changed it to the following day, i queired about my reserved seats and i was told that they will look into it and if those seats are available then it will be booked for me but they will get back to me. they didnt get back to me and i had to take whatever seat was allocated to me. so why hasnt anybody contacted me still and why is it that i have to lose out on my seat booking instead of at least getting compensated for the inconvenience in changing my flight because kulula cancelled the flight.