I am being charged more money to rebook ticket

Hello people<br> <br> I booked a greyhound ticket for someone at parkstation for the Harare to Johannesburg route in early November for R495. The person couldn't not make it so i changed the ticket to 25 November. Today i went back to greyhound offices at park station to have the date of departure changed to 3 December and was told i had to pay an additional R230 because the price is R730 for the 3rd of December. I then asked to downgrade to citiliner and was told that i had to cancel the greyhound ticket first which would make the ticket worth R396 because the cancellation fee is 20% , then add R49 to book on the citiliner which cost R445. <br> <br> How is this fair ? i feel that i am entitled to changed the date to the 3 rd of December without incurring any further costs and at the same time retaining the greyhound seat i had already booked