Bad customer service

I went in to buy medication and decided to also buy Calcium supplements which were priced R142.00 on the shelves. When I go to the till, the cashier told me I had to pay almost double the price. When I asked why he said the price was wrong. I asked for the manager in charge. He came and also told me I had to buy it with the price on the till. He told me to "go and buy it elsewhere". He even wrote his name down for me (Kwena ****edi). Saying "in case you forget". I'm a regular customer at this pharmacy because it's next to my place but the service I received made me change my mind altogether.