Bad service

I bought a pair of all terrain shoes on a sale on the 30th May 2020 at the Mall of Africa store. They have both developed a hole on the top of the shoe. I took them back only to be told they will take them back but to get replacement shoes I would have to pay in the difference between what I paid and a new pair of shoes. I find this totally unacceptable they have a 6 month guarantee on their shoes but I can't get new shoes and I now need to keep shoes with a hole on the top of both of them.