No return and no exchange after 7 days at Carrims Pretoria- am very disappointed and never buying from them

We went to K Carrim in Pretoria store and bought the tiles on special and when we had excess material they refused to take the tiles back. I think is unfair that they cannot buy their own product back. they have a small clause that after 7 days you cannot return their products, and our installation took more that 2 weeks to finish. what do they suggest we do with the 7 boxes of tiles? no shop wants to buy them and it is also unfair to expect them to buy products that are not theirs. if you may advise on what to do please come through.