Very clunky experience makes no sense

If I buy something from Takealot, I can pay with my a Discovery Miles and pay the balance with a credit card. I can also pay with vouchers and pay the balance with a credit card. I cannot pay with Discovery Miles and a voucher.

Why can't I? This is decades behind the rest of the world. I also have no way to cancel after I click Cash as the payment method - even by accident. I contacted Takealot through their portal but they only got back to me the next day after the order had been dispatched so I had to refuse to accept it so that it could be returned to their warehouse.

Where are the business processes that make sense in all of this? For an online business they are actually quite shoddy. The website is clunky and faulty (with filters and sorting), and the payment experience has giant holes in it and is as outdated as MS DOS.