Bad service

I bought a bread on the 20th of December at Spar - Mall of Tembisa. Today on the 21st of December when I was trying to eat that bread again, I found a green mold which caused me to actually check the expiry date which was the 15th of December. I took my receipt and the bread to Spar to bring it to their attention but unfortunately, I caught a rude lady's attention. Her name is Sarah. I tried to tell her what happened but she kept telling me how that was not possible, she said I probably picked that receipt and came Here to claim, she kept going on and on about how they'd never make such a mistake and how dare I even come to complain about that and she doesn't believe that I bought the bread from spar. She says she is 100% sure that they checked all breads and it's just not possible that they missed that one...she kept saying all these things just to make me look stupid because even how she said all this...she kept asking her friend whom she called "chomi" (was not wearing uniform so I'm not sure if she worked there) to confirm that they really check so that they prove a point to me. What hurts more is that I went there to make them aware but now I got there for them to be explaining to me how impossible it was. Not to even apologize once but I just left because clearly I was wasting my time. I believe I'm a valued customer whether I paid R1 or R1000 at a store and if I'm not happy then I have the right to let them know so that I can get value for my money...but what I got at Spar from Sarah's behavior was just another thing. Please help