Service is really poor

I took my Samsung S4 to MTN at Alexander four (4) weeks ago as it kept switching itself off every-time I was on watsapp or using the Internet. When I got there the guy who was assisting me advised that he could not assist me if I didn't have my paperwork. I understood and I went back home and collected my paperwork actually I brought back the packaging which the phone was delivered in. the guy who was assisting me told me that I did not need to bring everything and I explained to him that the first guy told me to bring it. He then advised that I should take the phone myself to their repair centre in Morning Site as it would be quicker, I told him I will not because I already wasted transport money by coming back again instead of being told that the first time I came in the morning. After two weeks without any communication I followed up on them only to find out that my phone is lying there at their repair centre without being fixed because I did not submit a proof of purchase please remember that I took everything to them initially & everything was in the box. Now it has been four weeks & after I followed up with them again they advised that my phone has not been fixed as yet.