Mango Airlines looks out for themselves

I am totally disappointed with Mango Airlines. I booked a ticked for my mum about a month ago for her to fly up to Johannesburg from Durban. She flew up on the 23rd April 2016 and was to fly back to Durban on the 2nd May 2016. Subsequent to that she has decided to stay on indefinitely. I called the call centre to see if I can possibly get a travel voucher so that when she decides which date she wants to fly back, we can then use the voucher to book it as opposed to booking another date for the sake of it and then having to change it again. I am fully aware that there is a penalty fee which I am prepared to pay but I would have to pay another penalty if I had to change the ticket again. I was told that the only time Mango Airlines can issue a voucher is when either a person cannot fly due to medical reasons, if the flight is delayed or if the flight is cancelled. In other words, only if it is to the benefit of the Airlines. This is absolute madness. We try to support Mango Airlines and then its when we need help, its a negative answer and no one can help. We are not asking for a refund. We are asking for a voucher which we can use later on with Mango Airlines. Once before I used Kulula Airlines and I had a similar problem and they assisted with crediting my travel bank account, which Mango Airlines does not possess. The only thing you have is a voucher system which works only for your airline’s benefit. Disappointed Frequent Flyer