Flysafair dishonest. Deducted way more than actual flight cost

Im extremely upset at FlySaFair, as they've ****** me with over R1000 rand. I initially booked a flight for 15 Jan 2023 at R1131, then changed the date to 8 Jan 2023, which then made the new cost of the flight R1799 in total. They then deducted the full R1799, instead of just deducting the difference, which was supposed to be almost R700. Now im struggling to get my money back. This is unacceptable and ****************.