Bad service

bought 2 items at the Foschini store the Grove mall amounting to R898.00 with a debit card last week during the week. The sizes were unfortunately small. I went to refund the items on Friday the 28th then I was told I cant be assisted because they don't have enough cash, I need to go to other stores or come back later. Today same thing happened, the cashier gave me bad attitude and the very same who seems to be a supervisor that didn't want to assist Friday was at the store today and acted like she never saw me on Friday. Today's cashier told me if they don't have enough cash they won't assist me. She was even talking me to in a very disrespectful manner. My question is, why do stores treat black customers differently. I had to waste my own time and petrol just to be given attitude. I won't shop again at Foschini the grove. They lack customer services skills. The only person who was speaking kindly to me is Ntombi and she failed to understand as well why was I told I cant be assisted on Friday. I wish a thorough follow up could be done especially for a supervisor and cashier that had so much attitude. Worse part when I left the store they laughed loudly.