No refund for faulty/incompatible ****le

I attended Cell C at Lakeside Mall on Monday, 14 September 2015 to get prepaid Mobile Broadband set up. I was told to buy a ZTE MF667 ****le, prepaid simcard and data. I asked the assistant, Kugiso, whether it would work on my Macbook. He assured me that it would and I bought it. I got home and the ****le did not work. <br> <br> I returned to the Cell C at Lakeside mall on Tuesday, 15 September 2015 with my Macbook to ask for assistance with the ****le. The assistant (name unknown) spent some time on my laptop trying to get the ****le to work but ultimately, could not produce any results. I requested a refund or exchange. The assistant told me that he would not do that until I had updated my laptop software. I repeatedly told him that the software could not be the issue because the requirements for the ****le were Mac 10.4.11 and later and my Mac was updated to 10.10.3. He would not listen and told me he would not proceed any further unless I came in with fully updated software.<br> <br> I felt that the sales assistant on Tuesday had a very poor and unhelpful attitude. I am also disappointed that I was badly advised and not given a refund. Please advise on where to go from here.