Ripping Customers off with flight costs

I have a flight booked for Monday 30th March 2020, and am able to change it to 23rd November 2020, via the online booking system. The new CHANGED ticket cost is suddenly R1 500-38. If I choose 23rd November 2020 and book a flight as NEW, the cost is suddenly R990.37. How is that possible, talk about a RIPE OFF.