My brother messed up his SPay Later payment, help pls

So my brother wanted to buy a pc for 4.5K, and he decided to use SPay Later to get a monthly installment for 12 months. However, the moment he clicked it, the bill instantly had an interest of nearly 25%, which resulted in a 5.5k total. Now that we know how expensive it became, is there a way to just cancel it by either paying a penalty fee or just waving it now? Or are there any other alternatives? Thanks

Additiona info: He was buying the pc in a physical store, but paid said shop with SPay Later since the shop has this option