Price difference from website to store

When I do my monthly grocery shopping, I go onto www.picknpay.co.za and check the prices of the products in order to work out my budget. I did this again this month. However, when I got to the store, 2 of the products had different prices in the store than on the website. ALL the other products had exactly the same price than on the website. I brought it to the attention of 2 ladies in the store and they just said that the prices on the website is for online shopping and not in the store. I don't understand how ALL the other prices can be the same, but not those 2 products. I am a bit unhappy that I wasn't assisted in buying the products at the price on the website. I am referring to the PnP long life milk, which was advertised as R50 for 6 boxes on the website, but in store it was R69-00. The other product was 1 kg Helios margarine, which was advertised as R21-80 on the website, but was R25-99 in the store. Nowhere on the website does it state that it is only online shopping prices.