Anti Cpmpeteive

Good day I have booked some time ago to benefit from lower prices for myslf and a colleague. Unfortunately, my circumstances have changed, and i can no longer use my booked flight. The colleague can fly. I tried to change the booking online but was advised by the call center agent, i cannot make that change online. Online changes are free. Then i asked for a voucher for the value i paid for the flights for myself only, but they want to dedcut R300 per flight which is now R600.

I am aware i agreed to their terms and conditions and you have no choice as if you disagree you cannot book the flight. This i would say is anti competive. Furthermore, maybe this is a case for the consumer watch dog. All i need is a voucher instead of change flight as i do not know when i will travel again.