The price on the shelf should be the price I pay

I don't know weather I'm right or wrong. But in all shops the price displayed on the shelf should be the price I pay.... We went to spar tops in lambertbaai bought 2 six packs of simnoff storm pine twist cans 440ml... It says on the price tag in front of the product 440ml cans R 63.50 and when we got to pay it scand R84.50... And I had told them the price on the shelf was R63.50 and she quickly told the boy that helps to change the price...and did not give the price displayed... I did not argue further because the store was busy and only had one teller open.... But I stand by I should have paid the the price display on the shelf..