Bad customer experiance: Return or exchange

I went to buy a calculator with a value of R299.99 at the CNA Cavendish square, Cape Town on the 12/02/2019, of which I then had to return as it didn't have the correct features for my functionality. I went back to the store yesterday with the slip in order to return the item and was told by the cashier that I will need to bring the packaging with in order to be refunded irrespective whether it has been opened, I went back home and brought the packaging with on the same day including the slip and requested for an exchange or a refund. Firstly, the store didn't have the item I wanted in stock and they offered me to a refund gift voucher with the value of R299.00, I didn't accept this initially as I insisted for cash to buy the item elsewhere and instead was placed in a position of no choice but have to wait until the stock is ordered from their N1 branch and that I will receive this by today. I called the store to cancel the order as I have now bought the item elsewhere(privately) with a less price and requested that I get a cash exchange for the voucher but the manager by the name Yumna was rude and gave me no chance to speak whatsoever until our call dropped. I feel that this is day ******* as I was given no choice but to take the voucher irrespective of the wait time, the back and forth, misinformation and the exclusion for classes that required the item I needed initially. I have been at many CNA stores around the country and have never had such a bad customer experience!!!!!!!