Vodacom misleading us into taking airtime advance as part of rewards

Vodacom has misleading UX on their gamified rewards program, I end up owing Vodacom airtime advance and no where am I notified that I’m taking an advance, the option states pay with airtime and shows my current balance and then I get an sms telling me I’ve taken a airtime advance however my balance is way larger than my purchase, if it is linked with my contract and airtime bought via prepaid they must state the difference because I now owe you money and I wouldn’t have purchased the offer if I knew it was on advance.