complaint

On Sunday the 7th April 2019, my Mother in law was suppose to take a flight from the OR Tambo Air Port to East London,the flight was leaving at 10:10am and upon arrival she was told the flight is full and they will refund her or she can take the next flight. no one cared for the reason why is taking the flight to east london, no body cared for the inconvenience they were causing her. and later on she was told oh you can go in the flight now there is space.i want to know how did SAA over booked the flight, i want formal letter of apology to her for the inconvenience, the employee who inconvenience her what is going to happen to that employee, my mother in law is not young woman, the embarrassment they caused her , where was the manager on duty because she was not even late for the flight.