They are refusing to refund me

I have recently bought a generator at Pick n pay Montana, I've used the generator a few times before it started giving me problems. I went to the store to return the item as it was still under warranty. They told me that they will first take it to their supplier to service and also check the fault. They took 3 weeks before returning the generator however when I finally got it back, nothing was done. I still couldn't use it. I went back to the store and was told that they won't refund me my money, they will just call the supplier again to check the fault. I collected the generator again and it's still not working. I am shocked and disappointed with service I received from that store as the manager refuses to exchange the item or refund me. I am tired of going back and forth to the store because they are not giving me any solutions.