No assistance for elderly

We had booked a flight for my mother of 74 from Jhb to Durban through Flysafair. We noticed afterwards that we could request assistance for her from the check in counter to her gate. We contacted the call centre to add this to her flight. We were asked if she had a wheelchair, and we said no, she is able to walk up the stairs to the plane, bit needs assistance through the airport as she is elderly and can only walk short distances. This was confirmed with the call centre agent, and the agent said it was added to her flight, as there was still assistance available. When she arrived there, they told her that it was not booked, and they couldn't help her. She had to walk all the way to the gate, which is quite a distance. She was tired and nearly collapsed.