wrongly advertised

On 2015-03-24I received a pamphlet for the special starting from 25 to 29 March 2015. I was so excited and went to shop to purchase Vodacom Smart Tab 3G advertised as R529 .90 only to be told the price in the catalogue is wrong after an invoice was issued to me to pay at the tills. While at the till I was told by the cashier to wait while she is going to fetch the items. I just need to know how is it possible that an item advertised and be told the price is wrong. How do I know in future that the items advertised are true or not. As a customer I believe the price you see is the price you pay. I would like to get a clarity on this matter as to why it was not explained to me that the price advertised is wrong after enquiring about the product and be told that the item is available then be issued with an invoice to pay. The manager then told me the store will encounter loss while I also lost my petrol. I require your assistance in this regard. Ref 716819