Hi-Fi Corporation *****ing from me and threatening me.

Today at 09:07 I purchased a computer monitor from Hi-Fi Corporation Newcastle for R1299. The monitor did not have an HDMI output as I needed, so I returned the monitor in exchange for an HDMI monitor. I had to pay in a difference of R399.10 at 11:43. The transaction was successful and I received an SMS confirming the purchase. However, the staff at Hi-Fi refused to give me the goods. In my mind, since I have made the purchase, the goods are no longer Hi-Fi corporation's property, but when I attempted to leave with it, the manager called security on me, stating that I didn't pay for the goods. They then made me pay that difference of R399.10 again. I received another SMS at 11:59 confirming the successful purchase of the third transaction. Again there was a hiccup with their system and again I could not leave with the goods I paid for. I eventually had to leave without a monitor and R2098 out of pocket. I feel cheated, ****** from and threatened by their manager and security. I had to purchase the monitor I needed elsewhere ( Thank you Rectron for giving me a good deal and releasing my goods for collection after payment)