Returned items but refused cash refund

I bought items at Precioux in Cresta. I kept 1 item and wanted to do exchanges. They did not have stock and I was told to come back. I went in the next week, still no new stock. i was told told to come in again. Went in sat 4 July for the second time to find no new stock. I was told that I have to take a credit note. I needed the money to buy a new item somewhere else. Now I was going to spend double my budget. I called Michelle on 6 july who is the manager. She said she was not authorised to give cash back, she would call the owner. I called her back on 7 july. The owner Penny Rodenhurst refused to give my money back. How do they get to keep my hard earned money > is it my fault that they do not have stock ?