Please solve my payment issues

I fly frequently with my four kids between Joburg and Cape Town. For the past two years or so, I have not been able to make payment online to kulula, which is my preferred carrier. I go through the laborious process of finding the right flight, filling out the details of all six my family members and then I try to pay with my FNB Visa cheque card. For the past year or two, for no reason I can discern, my payment has been rejected. Also my SAA Voyager Amex card, also my Capitec Mastercard. Also my husband's FNB checque card. I have asked the call centre about it, I have asked my bank about it. Nothing. Today, again, I tried booking a flight and opted to make an SID payment to avoid the card rejection. Only to find that Capitec is not a listed bank. Then the call centre tells me they also don't accept Capitec cards. I don't have R6000 cash to go and pay in Shoprite, within 1 hour, as the call centre agent suggested. I also don't have enough money in my FNB account until tomorrow. I would like to just give up on Kulula, but they are a good airline, with good prices. I'd rather solve the problem.