Pathetic customer service

I went to Clicks with an adverti*****t of the spring beauty specials. I saw that the prices on the shelves didn't correspond with specials so I spoke to one of the floor staff who then called the manager. After staying behind the till, continuing to ring up more customers, she eventually made her way to me. I showed her my screenshot of the ad and she didn't believe me. Told me I must not have read the ad properly. I went on the Internet and showed her the special is valid until 20 Oct 2015. She then still refused to give me the products for promo price and told me to go phone customer care myself and sort it out. I then insisted she phone customer care in store. I spent another 5min on the phone explaining myself and being put on hold. Meanwhile the other manager on duty has spoken to this lady and confirmed the special. Still she never helped me. I continued with my shopping leaving her to deal with customer care. After 35min in store and only after customer care spoke to her, she was forced to give me the product for the promo price advertised. Pathetic service! Why does a customer have to provide prove that an ad is valid? Not once did she apologise or take onus upon herself