Bad Service, steeling from clients

Never pay with a gift card at Woolworth, I told Woolworth's Brentwood parks casher that I still have R180 on my card, then she asked me that she will check the balance and then she stated do you want to buy cash and never gave me the card back. I counted all the items I brought and it was not more than the amount she told me I am owing the amount was R177. Are you paying your cashiers to little that the feel that they can do it to customers.