Refuse to give me refund for incorrect order

I asked for a refund on the day I made an order because my order was incorrect. Only a partial refund was given. When I followed up on it, they said that the refund had been processed and would reflect in my account within a few working days. After waiting a few working days and not seeing the rest of the amount refunded, I followed up, only to be told that because the order had been made more than 48 hours before, they could not process the refund. Despite the fact that I did request the refund within 48 hours of the order originally, they refuse to refund me the rest of the amount.