Delayed flights cost more that R60

Last Monday my parents-in-law were due to leave on a 6am flight from Johannesburg to Durban. The reason for selecting the earliest flight is so that they could arrive on time to open their business to their staff as they have tight deadlines. They were notified a little while before they were due to board that the flight was delayed without any indication of a new departure time, this flight only took off at 9:45, almost 4hours later. They had to inform all staff who had been waiting since 7am to go home, and unfortunately had to close their business for the day. They were given a R60 meal voucher to compensate for the loss of thousands of rands. The reason we choose Mango is because they were known to be relatively good when keeping to schedule. I do understand that emergencies arise and their safety is of the uttermost concern but 4hrs is really unacceptable. Why do you have travellers details if you cant give them adequate notice.