Items being sold at a high price compared to what it is being advertised

I was at the randburg branch and bought a box wine which was advertised at R84.99 but was over charged by R97.00 and was charged for a plastic bag which I did not even received. The liquor store advised they cannot help me with my refund and advised me to go the food section and when I went there with my ship and price the manager took her own time to assist me. they then requested me to complete a refund slip which i think was very unfair as it was not my fault they over charged me ,its their fault .when you have promotions update your systems and do not make it a customers problem .if i did not pick up the error no one was going to realize the price was wrong . i advised i do not want long stories I will rather have a full refund as a customer i need to be charged as the price advertised and if it not my fault why should i wait so long ?