PayJustNow (Pty) Ltd

Sign up for pay just now and decided to shop online and upon checking out my order it redirected me to PayJustNow page and required me to add card or banking details in my mind i am thinking of the re-payment and how they will debit only for them to debit the whole amount same time in my account.. This is not the agreement and how PayJustNow work why is it happening like this?