Kulula disappointment

I booked and paid for a flight from Cape Town to OR Tambo and a separate return flight from Lanseria to Cape Town on 21 June 2019. 2 days later I needed to change my flight to OR Tambo but to do so would cost more than just booking a new flight. There was no where online where I could cancel the original flight so I left it as it was, assuming that when I didn't show that Kulula would probably give my seat to another traveler anyway but if not they still received payment so what difference would it make to them anyway. On 3 July when I realised that my return ticket was going to need to change as well I went online to change the Lanseria to Cape Town leg which cost me an additional R414. The money came off my account but I never received confirmation so I called Kulula today only to hear that due to me not calling the call centre to cancel my original flight to OR Tambo I can no longer use the return ticket from Lanseria! To add to this the additional cost of R414 for the change I made for the return flight are also now non refundable. I cannot understand how or why they get away with this and am extremely disappointed with the fact that this information is not clearly communicated and highlighted to customers. Poor customer service so be warned. I feel like Kulula has ripped me off.