Charged more than the advertised price

Yesterday I asked my mom to help me out by going to buy my baby's Pampers Premium pants (Size 5) which were priced for R219.99 and I advised her to also get the 3 for 2 promotion on the Doom pesticide spray, however on returning my mother only returned with the nappies as she was charged R265.87 and despite informing the cashier that they were the incorrect price they went ahead and charged her the amount instead of verifying the price as per customers information. Instead they told my mom that I can come back if I was charged incorrectly as if I have the money or time to go deal with their incompetence because this would have been easily sorted right there had someone decided to do their job or even go as far as offer a good customer service by verifying the price which is even on the Clicks App when checking for prices or buying online. I have since been trying to get through their store number with no luck and I cancelled everything that in my basket to shop online for the Johnson & Johnson items which were way over R600 because this is ****************. This kind of incompetence is sickening and the fact that they responded with such a careless answer as if my only task is to run around to their store because of their lack of service is making me furious.