No repair or refund from Cashcruzaders

I've bought an angle grinder from Cashcruzaders Brakpan on the day I bought it at test it worked. I used it for ten minutes on the day it worked fine because it was very light work cutting thine aluminum plate. A month later while cutting steel pipes, using it for an hour it became hot and could see it was giving trouble. I took it in for repairs after a month in repairs tgey weren't finished they promised to phone me when I fetched it a week ago they blamed me for rust inside it. They didn't fix it, after much agotiation they want to sell me an inferior brand at discount no refund. My ascertion the Bosch angle grinder was rusted when I bought it, tgey nor me opened it after purchase. If worked on it it would have vouded the warantee. It could work if rusted but in light work. But normal work expired it now they won't refund me, while I've bought thousands of rands of stuff from them previously. Although the staff is friendly. I want to warn fo not by pawned or secondhand stuff from Cashcruzaders Brakpan. Rather by new stuff from game or takealot.