Ackermans Woodmead Unfair Return Policy

I bought an electronic item at Arkemans Woodmead, Sandton, Johannesburg. The item was bought on 19/05/2018 at 14:40pm. This item has problems with the battery as it does not last long. I returned to the store on 26/05/2018 at 12:30. I was advised that i can not return the item as it was after 7 days of purchase. I feel cheated because a day is worth 24 hours and i only got the phone from 19/05/2018 at 14:40pm not the whole day. This is unfair practice towards a consumer as i now have to own an item i do not want. I was told that my day started on the 19/05/2018 and according to common practice a day is made of 24 hours and i arrived in the store at 12:30 on 26/05/2018 and not after 14:40 as per purchase.