FLM ... more like *** !?!

Rye [email protected] (promotion) + 2x Banana [email protected] each (less 50%). Arrive at till and cashier requests override for Banana Bread. Price adjusted. I point out Rye bread scans wrong [email protected]. Override requested by supervisor. Override apparently done and total price is now R20 more ?! Supervisor says I must pay incorrect price in order to be refunded. I ask supervisor the total of 18.99 + 14.99...she responds "I don't know'...if you are not able to do basic arithmetic, why are you employed as a supervisor ?! Cashier takes initiative to add total and to this I request that supervisor stops wasting my time and take the correct amount of money, to which she refuses and insists on calling someone else. I tell the cashier i will be leaving the store with the items and pay with the correct amount of money. This is not the first time something like this happens. I am not 'employed' to tell an organization how to operate however, making sure discounts reflect correctly and employing competent staff...that would be a 'safe bet'.