Total garage tried to rip me off

I went to the station to buy toilet roll. It showed that the price was R5. 50 when I got to the till I was charged R6. 50. I refused to pay the extra charge and the supervisor was called. He also did not understand why I did not want to pay the extra charge. He said to me Vat has increased so are the prices.

Although I try to explain to him that a customer pays for the prices they see on the stands and that they need to change their prices on the stands. He still did not get it and gave me an attitude.

It's not about the R1 but the principle