unreasonable process

I bought electricity from the fnb app on two occasions. Unfortunately I the purchase was made from my credit card instead of my cheque account. I must say this isn't something I done intentionally. I just made the purchase to Find later it came off from my credit card. The issue with this is that I now miss out on ebucks I would have earned. I contacted fnb to request if the transaction can be reversed so that i can put it through on my cheque account but they said no. I don't understand why the app selects the credit card as the default account. I admit it was my mistake but it was caused by fnb cellphone app. I understand why they can't reverse the transaction because the vendor has been paid already but the least they can do is compensate me for the ebucks I should have earned. How many other people lost out on there ebucks due to this silly mistake made on the fnb app.