Airlink Unfair Business Practice

I would like to help me with this Booked a ticket from CPT to JHB and had to cancel. Got an credit for odd R6000 Now I want to fly to PE which is odd R2300 return They saying I may not use it for me and someone else. I have to use the full credit, even though it's less than half the credit I also have to pay a penalty of R500 So I must pay in effect R6500 for a ticket which is R2300 Surely this is unfair business practice, how can they do this. How many people over a year will loose money like this and they just getting the money for free and we must just accept it It will be millions over a year I really don't think this a fair practice I don't want the money back I just want to use what I paid for already Thank you Neels