False advertising! 10% Truloyalty advertising is actually 1%

Truworths is currently running a promotion that tru-royalty customers get 10% off certain items. I bought an item of R399 under this banner, upon checking the slip, I discovered that the 10% discount is actually 1%. Instead of the R39 off I was expecting, I only got R3.99 off. I showed the cashier and asked why its not 10% but she also said she doesnt understand since its generated by the system and that I must raise a query with head office. All Truwoths customers, please check your slips to ensure that promises made to you are kept by those we trust. Head office, please assist.