Forgot to take down this week only price

I went to Ackermans this morning and got some really nice deals, there was a price board hanging on top of a rack of curtains this week special. i took one of those curtains which is priced R129.99 but special price is R100.00. got to the till the cashier scanned the curtain and when i gave him the hundred rand he said its actually R129.99 so i said no the price on top of the curtains are a week special marked R100. he then left the till without saying anything and went to the back and called a supervisor. so they both took down the special board of the curtains, he then came back and said sorry they forgot to take down the special its not on special. just like that. forgot? so when something is on special, or marked down, is it? or should you stand in the line to wait and here its not and that they FORGOT to take down the speciail board this was absolutely the very last time i will shop at ackermans and i will not advise anybody who would want to shop there because of this reason, its very unprofessional to treat your customers that way i was treated this morning and a very bad look for the store indeed!