Booked and confirmed but could not fly

We booked my in-laws via Edgars on Mango and received an email confirming the booking from Mango. Just to arrive at the airport at 05:00 in the morning to be told sorry there is some issue with the ticket and we need to take it up with Edgars. WHY???? Mango sent us a confirmation email, not Edgars and if there is an issue with the payment from Edgars Mango should sort it out not us. Now my in-laws missed their daughters birthday because of some stuff up on the Mango and Edgars system. Why should we be inconvenienced for their system errors or what ever reason. Disappointing old folk is fine in SA it seems.