Lte data reversal

I attempted a top-up purchase of 20gbs which failed do to insufficient funds. I transferred funds and attempted another purchase which went through. Not long afterwards I received a message (for the 1st attempt) saying I can make payment within the next 15 days. With that message they have added an additional 20gbs to my account which I don’t need. I have spoken to sandy m and she said they can’t reverse the transaction. I made payment for the 20gbs which I wanted, I didn’t agree to continue with the 1st attempt as it was a failed attempt. I’m looking for a reversal of the data