The price I see should be the price I pay

Today I visited the Athlone branch. They were having a buy one get one free deal. So there was an error in pricing on four of my burgers amounting to about R20 each. At first the cashier took my packets and asked for it to be sent back as it was priced wrong. I then said is it my fault the pricing was wrong and asked to see the manager. The manager came who then said I could get the burgers for that price. My understanding is buy two and get the cheapest one free yes but I bought 4 different kinds of burgers so I still matched up the chargrilled burgers both at r64 for instance and the cheese burgers also both at R65 thinking that Way it makes it easier since I would be getting the 2nd packet of the same burger free. What the cashier then did was just scanned four of the larger priced burgers and didn't charge me for the four R20 packets. Had I known they were going to cheat me like this I would've paid individually. I only saw this when I got home so what was the point of the manager allowing me the mis priced item knowing they weren't going to charge me that price anyways. That's false advertising as well as misleading. They were the ones that made the mistake and the price the customer sees should be the price you pay. Busy Corner in Athlone u are a ******* and pathetic customer service. By calling the manager I actually thought he was linient he knew he was going to con me into believing I got it at that price. So disappointing