Unacceptable, multiple flight changes

Flights always delayed or moved. Booked a flight from CPT to JHB for 4:15pm, flight was changed to 6:20pm. On the morning of the flight I got notification of another change to 8:15pm. Arriving at the airport, another delay to 9:04pm, no notification from the airline. Travelling with 3 small children is near impossible at this time of night. Why do we pay for an early flight and then keep being moved to kater and later flights. Unacceptable!