MANGO charge Penalty plus revised flight charge for making change

Booked flight yesterday 10 Feb via Travelstart with Mango from Cape Town to Johannesburg to attend a funeral. Funeral was moved to next week. Changed the flight easily through Mango, however, I might as well booked a new flight for the price. Ridiculous price of R997 split into penalty of R390 plus new flight charges of R607. Had to change the Flysafair return flight as well and they only charged a penalty of R300 without charging me again for the new flight. I don't see why I had to pay again for the new flight at Mango if it was already paid for. The penalty should already cover it.