incorrect amount

I bought a jean and paid R105 but when I returned it I had to add extra amount because their system did not update the actual price of the jean. When I ask them who's fault is it they say it's the system's problem. I don't Ned to know I want the actual amount which I purchased for it. What if I had no money of adding that time, I'd be sitting with something I did not like. I was so disappointed and I am never buying anything at JET STORES. I always buy cash bt I will tell my friends and family not to purchase anything. I'm disgusted and nobody said sorry.