Complain of being charged by Incredible connection Greenstone 15% of purchase price when I returned items 1 day after purchase day

I bought a tablet Samsung Galaxy Tab S9 FE 5G at Incredible connection online store financed it with Happy Pay on the 14-September-2024 with collection Incredible connection Greenstone. The following day they arranged a different collection as they did not have a tablet instore. I collected the tablet at Incredible connection Eastgate on Sunday 15-September-2024. Same day I bought a Samsung Smart book cover at Incredible connection Greenstone. On Sunday I tested the tablet, to find out that it is not handling well in memory processing, I could not get satisfactory results on what I had bought it for, the following day Monday 16-September-2024 I had to return the tablet and the cover to Incredible connection Greenstone, both were in the original package, I was assisted by Neo and his manager. I was surprised that they said they could not refund me the full amount as the seal was broken, they were going to charge me 15%. According to the law I returned the item after 1 day of the purchase. Why should I loose 15%, Which law are they applying?