Over booked flight

I use Mango frequently as I reside in JHB & my daughter in DBN so we book her for all holidays. on the 25 May 2015 before school holidays I booked return tickets for her. Yesterday was her fly back to DBN on JE265 5.05pm flight.We standing at Mango long queues & a rep from mango tells us to go to another counter if we flying to DBN. Here at this counter there is a queue as well which is not moving. I later learn that Mango has over booked &amp