Overcharged Without Rational Explanation

I visited CTM Menlyn on Sunday 14 January to purchase tiles. I ordered 12 m2 of wall tiles as well as an additional 2 m2 of other tiles marked as costing R109.99/m2 (I have a photo of the tiles in question and the associated price. Upon paying for the tiles, i was shocked to see that i was charged nearly R2,400 for 2m2 of the tiles in question. The sales lady offered some lame excuse but could not explain why i was not charged R109.99/m2 for the tiles selected as marked on the show room floor. I cancelled the entire tile order of more than R6,200 as a result of this. I've not yet received a refund of the cancelled order

Surely a customer should be charged the marked price, and not an inflated price without explanation.

I will regretably not return.