Shoo i did not expect this from them

So i bought wors. As always there were two prices the original one then the less 15 price sticker. The cashier decided to charge me the original price n not the sale price but then my question is wasnt the sale price supposed to be loaded on the system already? This got me thinking to all the times i bought things with two prices at woolworths n kept wondering why my calculation was soo out. It never was out i was never charged the sale price but the original price. So y advertise the sale if you dont charge that amount or is it a way to get customers? I am disgusted at this finding especially because i always regarded Woolworths as one of the few stores that still upheld good standards n values. I am speechless